CN113678471A - Piezoelectric film, laminated piezoelectric element, and electroacoustic transducer - Google Patents
Piezoelectric film, laminated piezoelectric element, and electroacoustic transducer Download PDFInfo
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- CN113678471A CN113678471A CN202080024574.6A CN202080024574A CN113678471A CN 113678471 A CN113678471 A CN 113678471A CN 202080024574 A CN202080024574 A CN 202080024574A CN 113678471 A CN113678471 A CN 113678471A
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R17/00—Piezoelectric transducers; Electrostrictive transducers
- H04R17/005—Piezoelectric transducers; Electrostrictive transducers using a piezoelectric polymer
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R17/00—Piezoelectric transducers; Electrostrictive transducers
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
- H10N30/04—Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning
- H10N30/045—Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning by polarising
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
- H10N30/05—Manufacture of multilayered piezoelectric or electrostrictive devices, or parts thereof, e.g. by stacking piezoelectric bodies and electrodes
- H10N30/057—Manufacture of multilayered piezoelectric or electrostrictive devices, or parts thereof, e.g. by stacking piezoelectric bodies and electrodes by stacking bulk piezoelectric or electrostrictive bodies and electrodes
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/704—Piezoelectric or electrostrictive devices based on piezoelectric or electrostrictive films or coatings
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- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
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- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
- H10N30/852—Composite materials, e.g. having 1-3 or 2-2 type connectivity
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- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/88—Mounts; Supports; Enclosures; Casings
- H10N30/883—Additional insulation means preventing electrical, physical or chemical damage, e.g. protective coatings
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- Acoustics & Sound (AREA)
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- Composite Materials (AREA)
- Materials Engineering (AREA)
- Piezo-Electric Transducers For Audible Bands (AREA)
Abstract
The present invention addresses the problem of providing a piezoelectric film that has excellent flexibility in a high-temperature environment exceeding 50 ℃ and that exhibits good flexibility even at room temperature, a laminated piezoelectric element obtained by laminating the piezoelectric film, and an electroacoustic transducer using the piezoelectric film or the laminated piezoelectric element. The piezoelectric thin film has a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix made of a polymer material, and electrode layers on both surfaces of the polymer composite piezoelectric body, and has a maximum value of 0.1 or more in a temperature range of more than 50 ℃ and 150 ℃ or less in a loss tangent at a frequency of 1Hz, which is obtained by dynamic viscoelasticity measurement, and a value of 0.08 or more at 50 ℃.
Description
Technical Field
The present invention relates to a piezoelectric film used for acoustic devices such as speakers and microphones, a laminated piezoelectric element obtained by laminating the piezoelectric film, and an electroacoustic transducer using the piezoelectric film or the laminated piezoelectric element.
Background
In recent years, studies have been made on flexible displays using flexible substrates such as plastic.
As a substrate of the flexible display, for example, patent document 1 discloses a flexible display substrate in which a gas barrier layer or a transparent conductive layer is laminated on a transparent plastic film.
The flexible display is advantageous in terms of light weight, thinness, flexibility, and the like, as compared with a display using a conventional glass substrate, and can be provided in a curved shape such as a column. Further, since it can be rolled up for storage, it is attracting attention as a display device for mounting an advertisement or a PDA (personal digital assistant) without impairing portability even if it is a large screen.
When such a flexible display is used as an image display device and an audio generating device which play audio together with an image, such as a television, an acoustic device for generating audio, i.e., a speaker is required.
Among them, as a conventional speaker shape, a funnel shape, a so-called cone shape, a spherical dome shape, or the like is common. However, if these speakers are built in the flexible display, the advantages of the flexible display, i.e., lightness or flexibility, may be impaired. Further, when a speaker is externally provided, it is inconvenient to carry, and it is difficult to provide the speaker on a curved wall surface, which deteriorates the aesthetic feeling.
Among them, as a speaker which can be integrated with a flexible display without impairing its lightweight property or flexibility, a piezoelectric film (an electroacoustic conversion film) described in patent document 2 is known.
The piezoelectric thin film comprises a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a viscoelastic matrix made of a polymer material having viscoelasticity at normal temperature, thin film electrodes formed on both surfaces of the polymer composite piezoelectric body, and a protective layer formed on the surface of the thin film electrode, and has a maximum value in which the loss tangent at a frequency of 1Hz is 0.1 or more, which is obtained by dynamic viscoelasticity measurement, within a temperature range of 0 to 50 ℃.
Prior art documents
Patent document
Patent document 1: japanese patent laid-open No. 2000-338901
Patent document 2: japanese laid-open patent publication No. 2015-29270
Disclosure of Invention
Technical problem to be solved by the invention
In order to use the piezoelectric film as a speaker, it is necessary to convert a stretching motion along the film surface into vibration of the film surface. Since the conversion from the stretching motion to the vibration is realized by holding the piezoelectric film in a bent state, the piezoelectric film can be made to function as a speaker.
However, it is known that the lowest resonance frequency f of the diaphragm for a speaker0Is given by the following formula. Where s is the stiffness of the vibration system and m is the mass.
[ numerical formula 1]
Lowest resonance frequency:
at this time, the minimum resonance frequency f is the lowest resonance frequency because the mechanical stiffness s is reduced as the degree of bending of the piezoelectric thin film, that is, the radius of curvature of the bending portion, is increased0And becomes smaller. I.e. the sound quality (volume) of the loudspeakerFrequency characteristics) change according to the radius of curvature of the piezoelectric film.
In view of the above, the piezoelectric film used as a speaker for a flexible display preferably has the following requirements.
(i) Flexibility
For example, when the paper is held in a state of being carried in a paper-like light roll such as a newspaper or magazine, the paper is constantly subjected to a relatively slow but large bending deformation of several Hz or less from the outside. In this case, if the piezoelectric thin film is hard, a large bending stress is generated, and cracks may be generated at the interface between the polymer matrix and the piezoelectric particles, and finally, the piezoelectric thin film may be broken. Therefore, the piezoelectric thin film is required to have appropriate flexibility. Further, if the strain energy can be diffused to the outside as heat, the stress can be relaxed. Therefore, the loss tangent of the piezoelectric thin film is required to be appropriately large.
(ii) Sound quality
The piezoelectric particles are vibrated at a frequency of an audio band of 20Hz to 20kHz, and the entire diaphragm (piezoelectric film) is vibrated by the vibration energy, so that the speaker plays sound. Therefore, in order to improve the transmission efficiency of the vibration energy, the piezoelectric thin film is required to have an appropriate hardness. When the frequency characteristics of the speaker are smooth, the lowest resonance frequency f0The amount of change in sound quality when the change is accompanied by a change in curvature is also small. Therefore, the loss tangent of the piezoelectric thin film is required to be appropriately large.
As described above, a piezoelectric film used as a speaker for a flexible display is required to be hard to 20Hz to 20kHz vibration and flexible to not more than 20Hz vibration. Further, the loss tangent of the polymer composite piezoelectric body is required to be appropriately large for vibrations of all frequencies of 20kHz or less.
The piezoelectric thin film described in patent document 2 satisfies the above conditions at normal temperature (0 to 50 ℃), and exhibits excellent flexibility and sound quality.
However, the environment in which the speaker is used is not limited to normal temperature, and may be used in a high temperature environment exceeding 50 ℃ depending on the country, region, and place of use. However, the piezoelectric thin film described in patent document 2 hardly exhibits sufficient flexibility and sound quality in a high-temperature environment exceeding 50 ℃.
The present invention has been made to solve the problems of the conventional techniques, and an object of the present invention is to provide a piezoelectric film having excellent flexibility in a high-temperature environment exceeding 50 ℃ and having good flexibility even at normal temperature, a laminated piezoelectric element obtained by laminating the piezoelectric film, and an electroacoustic transducer using the piezoelectric film or the laminated piezoelectric element.
Means for solving the technical problem
In order to achieve the above object, the present invention has the following structure.
[1] A piezoelectric thin film comprising a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix comprising a polymer material, and electrode layers formed on both surfaces of the polymer composite piezoelectric body,
the loss tangent at a frequency of 1Hz obtained by dynamic viscoelasticity measurement has a maximum value of 0.1 or more in a temperature range of more than 50 ℃ and 150 ℃ or less, and the value at 50 ℃ is 0.08 or more.
[2] The piezoelectric thin film according to [1], which has a protective layer provided on a surface of the electrode layer.
[3] The piezoelectric thin film according to [1] or [2], which is polarized in a thickness direction.
[4] The piezoelectric thin film according to any one of [1] to [3], which has no in-plane anisotropy in piezoelectric characteristics.
[5] The piezoelectric thin film according to any one of [1] to [4], which has an external lead for connecting the electrode layer with an external power source.
[6] A laminated piezoelectric element comprising 2 or more laminated piezoelectric thin films according to any one of [1] to [5 ].
[7] The laminated piezoelectric element according to [6], wherein the piezoelectric thin films are polarized in a thickness direction, and polarization directions of adjacent piezoelectric thin films are opposite.
[8] The laminated piezoelectric element according to [6] or [7], which is obtained by laminating 2 or more piezoelectric thin films by folding the piezoelectric thin films 1 or more times.
[9] The laminated piezoelectric element according to any one of [6] to [8], which has an adhesive layer for adhering adjacent piezoelectric films.
[10] An electroacoustic transducer having a vibration plate, the piezoelectric film of any one of [1] to [5], or the laminated piezoelectric element of any one of [6] to [9 ].
[11] The electroacoustic transducer according to [10], wherein a product of a thickness of the piezoelectric film or the laminated piezoelectric element and a storage modulus at a frequency of 1Hz and 25 ℃ obtained by dynamic viscoelasticity measurement is 0.1 to 3 times a product of a thickness of the vibrating plate and a Young's modulus.
[12] The electroacoustic transducer according to [10] or [11], wherein a product of a thickness of the piezoelectric film or the laminated piezoelectric element and a storage modulus at a frequency of 1kHz and 25 ℃ on a principal curve obtained by dynamic viscoelasticity measurement is 0.3 to 10 times a product of a thickness of the vibrating plate and a Young's modulus.
[13] The electro-acoustic transducer according to any one of [10] to [12], which has an adhesive layer for adhering the vibration plate and the piezoelectric film or laminating the piezoelectric element.
Effects of the invention
According to the present invention, there are provided a piezoelectric film having flexibility in a high-temperature environment exceeding 50 ℃ and having good flexibility even at normal temperature, a laminated piezoelectric element obtained by laminating the piezoelectric film, and an electroacoustic transducer using the piezoelectric film or the laminated piezoelectric element.
Drawings
Fig. 1 is a conceptual diagram of an example of the piezoelectric thin film of the present invention.
Fig. 2 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric thin film.
Fig. 3 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric thin film.
Fig. 4 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric thin film.
Fig. 5 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric thin film.
Fig. 6 is a conceptual diagram for explaining an example of a method for manufacturing a piezoelectric thin film.
Fig. 7 is a conceptual diagram of an example of a piezoelectric speaker using the piezoelectric film shown in fig. 1.
Fig. 8 is a conceptual diagram of an example of the electroacoustic transducer of the present invention using the laminated piezoelectric element of the present invention.
Fig. 9 is a conceptual diagram of another example of the laminated piezoelectric element of the present invention.
Fig. 10 is a conceptual diagram of another example of the laminated piezoelectric element of the present invention.
Fig. 11 is a conceptual diagram of another example of the laminated piezoelectric element of the present invention.
Fig. 12 is a conceptual diagram of another example of the laminated piezoelectric element of the present invention.
Fig. 13 is a conceptual diagram of another example of the laminated piezoelectric element of the present invention.
Fig. 14 is a conceptual diagram of another example of the laminated piezoelectric element of the present invention.
Fig. 15 is a conceptual diagram of another example of the laminated piezoelectric element of the present invention.
Fig. 16 is a conceptual diagram for explaining the protruding portion on the laminated piezoelectric element of the present invention.
Detailed Description
Hereinafter, the piezoelectric film, the laminated piezoelectric element, and the electroacoustic transducer according to the present invention will be described in detail with reference to preferred embodiments shown in the drawings.
The following description of the constituent elements is made in accordance with exemplary embodiments of the present invention, but the present invention is not limited to these embodiments.
In the present specification, the numerical range expressed by the term "to" means a range including numerical values before and after the term "to" as a lower limit value and an upper limit value.
Fig. 1 is a cross-sectional view conceptually showing an example of the piezoelectric thin film of the present invention.
As shown in fig. 1, the piezoelectric thin film 10 includes: a piezoelectric layer 20 which is a sheet having piezoelectricity, a lower electrode 24 laminated on one surface of the piezoelectric layer 20, a lower protective layer 28 laminated on the lower electrode 24, an upper electrode 26 laminated on the other surface of the piezoelectric layer 20, and an upper protective layer 30 laminated on the upper electrode 26.
The piezoelectric layer 20 is formed by dispersing piezoelectric particles 36 in a matrix 34 made of a polymer material. That is, the piezoelectric layer 20 is a polymer composite piezoelectric body in the present invention.
As described later, the piezoelectric thin film 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.
For example, in various acoustic apparatuses (acoustic devices) such as a speaker, a microphone, and a pickup used in a musical instrument such as a guitar, the piezoelectric film 10 is used to generate (reproduce) sound by vibration according to an electric signal or to convert vibration caused by the sound into the electric signal.
In addition, the piezoelectric thin film can be used for a pressure sensor, a power generating element, and the like.
As described above, the piezoelectric film used for a flexible speaker or the like preferably has good flexibility and sound quality.
That is, the piezoelectric thin film is required to be rigid against vibration of 20Hz to 20kHz and flexible against vibration of not more than logarithmic Hz. Further, the loss tangent of the piezoelectric film 10 is required to be appropriately large for vibrations of all frequencies of 20kHz or less.
Generally, a polymer solid has a viscoelastic relaxation mechanism, and it is observed that large-scale molecular motion appears as a decrease (relaxation) in storage modulus (young's modulus) or a loss of maximum (absorption) in elastic modulus with an increase in temperature or a decrease in frequency. Among them, relaxation caused by the micro brownian motion of molecular chains in the amorphous region is called primary dispersion, and a very large relaxation phenomenon can be found. The temperature at which this main dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism is most remarkably exhibited.
In the piezoelectric thin film 10 of the present invention, the maximum value at which the loss tangent (tan δ) at a frequency of 1Hz, which is obtained by dynamic viscoelasticity measurement, is 0.1 or more is 1 or more in a temperature range of more than 50 ℃ and 150 ℃. In the piezoelectric thin film 10 of the present invention, the value of loss tangent at 50 ℃ at a frequency of 1Hz as measured by dynamic viscoelasticity is 0.08 or more.
Therefore, the piezoelectric thin film 10 of the present invention has very high flexibility in a high temperature environment exceeding 50 ℃, and also has good flexibility at normal temperature. The piezoelectric thin film 10 of the present invention is hard to vibrate at 20Hz to 20kHz in a high temperature environment exceeding 50 ℃, and flexible to vibrate slowly at a frequency of not more than logarithmic Hz.
In the present invention, "normal temperature" means a temperature range of about 0 to 50 ℃.
The piezoelectric layer 20 is formed by dispersing piezoelectric particles 36 in a matrix 34.
As an example, as the substrate 34 of the piezoelectric layer 20 (polymer composite piezoelectric body), a mixed polymer material in which a polymer material having a glass transition point at room temperature and a polymer material having a glass transition point exceeding 50 ℃ are mixed is used as the piezoelectric thin film 10 of the present invention.
The polymer material having a glass transition point at normal temperature is a polymer material having viscoelasticity at normal temperature. On the other hand, a polymer material having a glass transition point of more than 50 ℃ is a polymer material having viscoelasticity in a temperature range of more than 50 ℃.
By using such a mixed polymer material as the base 34 of the piezoelectric layer 20, the piezoelectric thin film 10 in which the loss tangent at a frequency of 1Hz, which is obtained by dynamic viscoelasticity measurement, has a maximum value of 0.1 or more in a temperature range of more than 50 ℃ and 150 ℃ or less, and a value at 50 ℃ is 0.08 or more can be obtained.
In the piezoelectric thin film 10 of the present invention, the maximum value at which the loss tangent at a frequency of 1Hz obtained by dynamic viscoelasticity measurement reaches 0.1 or more is 1 or more in a temperature range of more than 50 ℃ and 150 ℃.
Therefore, the piezoelectric thin film 10 of the present invention can effectively diffuse strain energy as heat to the outside when the piezoelectric thin film 10 is gently bent by an external force in a high temperature environment exceeding 50 ℃. Therefore, in the piezoelectric thin film 10, the stress concentration at the interface between the substrate 34 and the piezoelectric particles 36 in the maximum bending moment portion is relaxed, and cracks can be prevented from occurring at the interface between the substrate 34 and the piezoelectric particles 36. As a result, the piezoelectric thin film 10 of the present invention has very high flexibility against slow motions due to external forces such as bending and rolling performed by a user in a high-temperature environment exceeding 50 ℃. In the above respect, the same applies to the laminated piezoelectric element and the electroacoustic transducer described later.
The maximum value of the loss tangent in the temperature range of more than 50 ℃ and not more than 150 ℃ at a frequency of 1Hz is preferably 0.3 or more, more preferably 0.5 or more.
The maximum value at which the loss tangent at a frequency of 1Hz becomes 0.1 or more may be present in a plurality of numbers in a temperature range of more than 50 ℃ and 150 ℃.
In the piezoelectric thin film 10 of the present invention, the value of loss tangent at 50 ℃ at a frequency of 1Hz as measured by dynamic viscoelasticity is 0.08 or more.
The use environment of the piezoelectric thin film 10 is not limited to a high temperature environment exceeding 50 ℃. The piezoelectric thin film is manufactured by a manufacturing method involving winding, for example, roll-to-roll, and the temperature of the manufacturing environment is usually room temperature. Therefore, the piezoelectric thin film 10 is also required to have a certain degree of flexibility in a room temperature environment.
In contrast, in the piezoelectric thin film of the present invention, the loss tangent at a frequency of 1Hz and 50 ℃ is 0.08 or more in addition to the maximum value of the loss tangent in the high temperature range, and therefore, for the same reason as described above, the piezoelectric thin film exhibits good operability and good flexibility applicable to various production methods even in a normal temperature environment. In the above respect, the same applies to the laminated piezoelectric element and the electroacoustic transducer described later.
The loss tangent at 50 ℃ and a frequency of 1Hz is preferably 0.10 or more, more preferably 0.15 or more.
In the piezoelectric thin film 10 of the present invention, the maximum value of the loss tangent at 1Hz may or may not be present in the temperature range of normal temperature.
In addition, in the piezoelectric thin film 10 of the present invention, the maximum value of the loss tangent at 1Hz is 1 or more in the temperature range of the normal temperature, and thus the flexibility of the piezoelectric thin film 10 in the normal temperature environment can be further improved. In the piezoelectric thin film 10 of the present invention, when the maximum value of the loss tangent at 1Hz is present in the temperature range of normal temperature, the maximum value of the loss tangent is preferably 0.08 or more.
As described above, in the piezoelectric thin film 10 of the present invention, a mixed polymer material of a polymer material having viscoelasticity at normal temperature and a polymer material having viscoelasticity in a temperature range exceeding 50 ℃ is used as the base 34 of the piezoelectric layer 20.
As the polymer material having viscoelasticity at normal temperature, various known polymer materials can be used as long as they have dielectric properties. The polymer material preferably has a loss tangent maximum value at a frequency of 1Hz of 0.08 or more at room temperature in a dynamic viscoelasticity test.
Therefore, when the piezoelectric thin film 10 is gently bent by an external force at normal temperature, stress concentration at the interface between the substrate 34 and the piezoelectric particles 36 in the maximum bending moment portion is relaxed, and favorable flexibility can be obtained.
In the polymer material having viscoelasticity at room temperature, the storage modulus (E') at a frequency of 1Hz as measured by dynamic viscoelasticity is preferably 100MPa or more at 0 ℃ and preferably 10MPa or less at 50 ℃.
Therefore, the bending moment generated when the piezoelectric thin film 10 is gently bent by an external force can be reduced, and the piezoelectric thin film can exhibit rigidity against acoustic vibration of 20Hz to 20 kHz.
Further, a polymer material having viscoelasticity at room temperature is more preferably one having a relative permittivity of 10 or more at 25 ℃. Therefore, when a voltage is applied to the piezoelectric thin film 10, a higher electric field is applied to the piezoelectric particles in the matrix, and thus a larger amount of deformation can be expected.
However, in view of ensuring good moisture resistance, a polymer material having a relative dielectric constant of 10 or less at 25 ℃ is also preferable.
Examples of the polymer material having viscoelasticity at room temperature satisfying such conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA (CR-V)), polyvinyl acetate, poly (vinylidene chloride-co-acrylonitrile), polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl acrylate. Further, as these polymer materials, commercially available products such as HYBRAR 5127 (manufactured by KURARAY co., ltd) can be preferably used. Among them, as a polymer material having viscoelasticity at normal temperature, a material having a cyanoethyl group is preferably used, and especially, a cyanoethylated PVA is preferably used.
In addition, only 1 kind of these polymer materials may be applied, or a plurality of kinds may be used (mixed) at the same time.
The mixed polymer material is a polymer material having a glass transition point of more than 50 ℃ in which a polymer material having viscoelasticity at normal temperature is mixed, that is, a polymer material having viscoelasticity in a temperature range of more than 50 ℃. In the following description, for convenience, the "polymer material having viscoelasticity in a temperature range exceeding 50 ℃ is also referred to as" polymer material having viscoelasticity at high temperature ".
In the piezoelectric thin film 10 of the present invention, a polymer material mixture in which a polymer material having viscoelasticity at normal temperature is mixed with a polymer material having viscoelasticity at high temperature is used as the base 34 constituting the piezoelectric layer 20, and thus the glass transition point of the base 34 is increased, and excellent flexibility in a high-temperature environment exceeding 50 ℃ and good flexibility in a normal-temperature environment are both satisfied.
As the polymer material having viscoelasticity at high temperature, various materials can be used as long as the polymer material has a glass transition point exceeding 50 ℃ and has dielectric properties.
As an example, cyanoethylated polyglucose (CR-S) and the like can be exemplified.
The amount of the polymer material having viscoelasticity at high temperature added to the base 34 constituting the piezoelectric layer 20 is not limited to a specific amount at normal temperature.
In the mixed polymer material in which the polymer material having viscoelasticity at normal temperature and the polymer material having viscoelasticity at high temperature are mixed, the amount of the polymer material having viscoelasticity at high temperature is preferably 31 to 80% by mass, more preferably 41 to 70% by mass, and further preferably 51 to 60% by mass.
By setting the amount of the polymer material having viscoelasticity at high temperature to 31 mass% or more, the effect of adding the polymer material having viscoelasticity at high temperature is exhibited appropriately, and it is preferable that the piezoelectric thin film 10 exhibiting excellent flexibility in a high temperature environment exceeding 50 ℃.
By setting the addition amount of the polymer material having viscoelasticity at high temperature to 80 mass% or less, flexibility at normal temperature can be improved.
For the purpose of adjusting the dielectric properties or mechanical properties, other dielectric polymer materials may be added to the substrate 34 as necessary, in addition to the polymer material having viscoelasticity at normal temperature and the polymer material having viscoelasticity at high temperature.
For the purpose of adjusting the glass transition point, in addition to the dielectric polymer material, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, and thermosetting resins such as phenol resin, urea resin, melamine resin, alkyd resin, and mica may be added to the substrate 34.
Further, a tackifier such as rosin ester, rosin, terpene phenol, and petroleum resin may be added for the purpose of improving adhesiveness.
The piezoelectric layer 20 is a polymer composite piezoelectric body in which the piezoelectric particles 36 are dispersed in the matrix 34.
The piezoelectric particles 36 are ceramic particles having a perovskite or wurtzite crystal structure.
Examples of the ceramic particles constituting the piezoelectric particles 36 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), and barium titanate (BaTiO)3) Zinc oxide (ZnO), barium titanate and bismuth ferrite (BiFe)3) And solid solution (BFBT) of (a).
Only 1 type of these piezoelectric particles 36 may be applied, or a plurality of types may be used (mixed) at the same time.
The particle diameter of the piezoelectric particles 36 is not limited, and may be appropriately selected according to the size, application, and the like of the piezoelectric thin film 10.
The particle diameter of the piezoelectric particles 36 is preferably 1 to 10 μm. By setting the particle diameter of the piezoelectric particles 36 to be in this range, the piezoelectric thin film 10 can obtain preferable results in terms of compatibility between high piezoelectric characteristics and flexibility.
In fig. 1, the piezoelectric particles 36 in the piezoelectric layer 20 are uniformly and regularly dispersed in the matrix 34, but the present invention is not limited thereto.
That is, the piezoelectric particles 36 in the piezoelectric layer 20 may be dispersed irregularly in the matrix 34 as long as they are uniformly dispersed.
In the piezoelectric thin film 10, the amount ratio of the matrix 34 to the piezoelectric particles 36 in the piezoelectric layer 20 is not limited. The amount ratio of the matrix 34 and the piezoelectric particles 36 in the piezoelectric layer 20 may be appropriately set depending on the size and thickness of the piezoelectric film 10 in the surface direction, the application of the piezoelectric film 10, the required characteristics of the piezoelectric film 10, and the like.
The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, and more preferably 50% or more. Therefore, the volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is more preferably 50 to 80%.
By setting the amount ratio of the matrix 34 to the piezoelectric particles 36 to the above range, preferable results can be obtained in terms of compatibility between high piezoelectric characteristics, flexibility, and the like.
The thickness of the piezoelectric layer 20 in the piezoelectric thin film 10 is not limited, and may be appropriately set according to the application of the piezoelectric thin film 10, the required characteristics of the piezoelectric thin film 10, and the like. The thicker the piezoelectric layer 20 is, the more advantageous the rigidity such as toughness of the sheet is, but the larger the voltage (potential difference) required to stretch the piezoelectric film 10 by the same amount is.
The thickness of the piezoelectric layer 20 is preferably 10 to 300. mu.m, more preferably 20 to 200. mu.m, and still more preferably 30 to 150. mu.m.
By setting the thickness of the piezoelectric layer 20 to the above range, preferable results can be obtained in terms of both ensuring rigidity and appropriate flexibility.
In the piezoelectric film 10 of the present invention, for the same reason as that of the piezoelectric film 10, it is preferable that the piezoelectric layer 20 (polymer composite piezoelectric body) has 1 or more maximum values of 0.1 or more loss tangent at a frequency of 1Hz, which are obtained by dynamic viscoelasticity measurement, in a temperature range of more than 50 ℃ and 150 ℃. The maximum value of the loss tangent in the piezoelectric layer 20 at a frequency of 1Hz and in a temperature range of more than 50 ℃ and not more than 150 ℃ is preferably 0.3 or more, and more preferably 0.5 or more.
In the piezoelectric layer 20, a maximum value at which the loss tangent at a frequency of 1Hz becomes 0.1 or more may be present in a plurality of numbers in a temperature range of more than 50 ℃ and 150 ℃.
In the piezoelectric film 10 of the present invention, for the same reason as that of the piezoelectric film 10, the value of the loss tangent at a frequency of 1Hz in the piezoelectric layer 20 obtained by dynamic viscoelasticity measurement at 50 ℃ is preferably 0.08 or more.
The loss tangent at 50 ℃ and a frequency of 1Hz in the piezoelectric layer 20 is preferably 0.07 or more, more preferably 0.1 or more.
Further, in the piezoelectric layer 20 of the piezoelectric thin film 10 of the present invention, the maximum value of the loss tangent at 1Hz may or may not be present in the temperature range of normal temperature.
However, for the same reason as that for the piezoelectric thin film 10, it is preferable that the piezoelectric layer 20 has 1 or more maximum values of loss tangent at 1Hz in the temperature range of normal temperature. In the piezoelectric layer 20, when the maximum value of the loss tangent at 1Hz is within the temperature range of normal temperature, the maximum value of the loss tangent is preferably 0.08 or more.
As shown in fig. 1, the illustrated piezoelectric film 10 has the following structure: the piezoelectric layer 20 has a lower electrode 24 on one surface thereof and a lower protective layer 28 on the surface thereof, and has an upper electrode 26 on the other surface thereof and an upper protective layer 30 on the surface thereof. The upper electrode 26 and the lower electrode 24 form an electrode pair.
In addition to these layers, the piezoelectric film 10 has, for example, electrode lead-out portions for leading out electrodes from the upper electrode 26 and the lower electrode 24, and the electrode lead-out portions are connected to the power supply PS. Also, the piezoelectric film 10 may have an insulating layer or the like that prevents short circuits or the like by covering the region exposed by the piezoelectric layer 20.
That is, the piezoelectric thin film 10 has the following structure: the piezoelectric layer 20 is sandwiched between the upper electrode 26 and the lower electrode 24, which are electrode pairs, and the laminate is sandwiched between the lower protective layer 28 and the upper protective layer 30.
In this way, in the piezoelectric thin film 10, the region sandwiched by the upper electrode 26 and the lower electrode 24 is stretched in accordance with the applied voltage.
In the piezoelectric thin film 10, the lower protective layer 28 and the upper protective layer 30 are not essential components, and are preferably provided.
The lower protective layer 28 and the upper protective layer 30 cover the upper electrode 26 and the lower electrode 24 and provide the piezoelectric layer 20 with appropriate rigidity and mechanical strength. That is, in the piezoelectric thin film 10, the piezoelectric layer 20 composed of the base 34 and the piezoelectric particles 36 exhibits very excellent flexibility against slow bending deformation, but on the other hand, the rigidity or mechanical strength may be insufficient depending on the application. To compensate for this deficiency, a lower protective layer 28 and an upper protective layer 30 are provided in the piezoelectric film 10.
The lower protective layer 28 and the upper protective layer 30 are not limited, and various sheet-like materials can be used, and various resin films can be preferably exemplified as an example.
Among them, a resin film made of polyethylene terephthalate (PET), polypropylene (PP), Polystyrene (PS), Polycarbonate (PC), Polyphenylene Sulfide (PPs), polymethyl methacrylate (PMMA), polyether imide (PEI), Polyimide (PI), polyethylene naphthalate (PEN), cellulose Triacetate (TAC), a cycloolefin resin, or the like is preferably used for reasons such as excellent mechanical properties and heat resistance.
The thicknesses of the lower protective layer 28 and the upper protective layer 30 are also not limited. The thicknesses of the lower protective layer 28 and the upper protective layer 30 are substantially the same, but may be different.
However, if the rigidity of the lower protective layer 28 and the upper protective layer 30 is too high, the flexibility is impaired as well as the stretching of the piezoelectric layer 20 is restricted. Therefore, in addition to the case where mechanical strength and good workability as a sheet are required, it is advantageous that the lower protective layer 28 and the upper protective layer 30 are thinner.
In the piezoelectric thin film 10, when the thickness of the lower protective layer 28 and the upper protective layer 30 is 2 times or less the thickness of the piezoelectric layer 20, favorable results can be obtained in terms of both ensuring rigidity and appropriate flexibility.
For example, when the thickness of the piezoelectric layer 20 is 50 μm and the lower protective layer 28 and the upper protective layer 30 are made of PET, the thickness of the lower protective layer 28 and the upper protective layer 30 is preferably 100 μm or less, more preferably 50 μm or less, and still more preferably 25 μm or less.
In the piezoelectric thin film 10, the lower electrode 24 is formed between the piezoelectric layer 20 and the lower protective layer 28, and the upper electrode 26 is formed between the piezoelectric layer 20 and the upper protective layer 30.
The lower electrode 24 and the upper electrode 26 are provided to apply a driving voltage to the piezoelectric layer 20.
In the present invention, the material for forming the lower electrode 24 and the upper electrode 26 is not limited, and various conductors can be used. Specifically, carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, molybdenum, and the like, alloys thereof, laminates and composites of these metals and alloys, indium tin oxide, and the like can be exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide can be preferably exemplified as the lower electrode 24 and the upper electrode 26.
The method of forming the lower electrode 24 and the upper electrode 26 is not limited, and various known methods such as a vapor deposition method (vacuum film forming method) such as vacuum deposition and sputtering, a film forming method by plating, and a method of attaching a foil made of the above-described material can be used.
Among them, a thin film of copper, aluminum, or the like formed by vacuum deposition is particularly preferable as the lower electrode 24 and the upper electrode 26, for the reason that the flexibility of the piezoelectric thin film 10 can be secured. Among these, a copper thin film by vacuum deposition is particularly preferably used.
The thicknesses of the lower electrode 24 and the upper electrode 26 are not limited. The thicknesses of the lower electrode 24 and the upper electrode 26 are substantially the same, but may be different.
However, similarly to the lower protective layer 28 and the upper protective layer 30, if the rigidity of the lower electrode 24 and the upper electrode 26 is too high, not only the stretching of the piezoelectric layer 20 is restricted, but also the flexibility is impaired. Therefore, the lower electrode 24 and the upper electrode 26 are advantageously thinner as long as the resistance is not excessively high. That is, the lower electrode 24 and the upper electrode 26 are preferably thin film electrodes.
In the piezoelectric thin film 10, it is preferable that the product of the thickness of the lower electrode 24 and the upper electrode 26 and the young's modulus is smaller than the product of the thickness of the lower protective layer 28 and the upper protective layer 30 and the young's modulus, because flexibility is not significantly impaired.
For example, in the case of a combination in which the lower protective layer 28 and the upper protective layer 30 are made of PET (Young's modulus: about 6.2GPa) and the lower electrode 24 and the upper electrode 26 are made of copper (Young's modulus: about 130GPa), if the thicknesses of the lower protective layer 28 and the upper protective layer 30 are set to 25 μm, the thicknesses of the lower electrode 24 and the upper electrode 26 are preferably 1.2 μm or less, more preferably 0.3 μm or less, and still more preferably 0.1 μm or less.
The storage modulus (E') of the piezoelectric thin film 10 at a frequency of 1Hz, which is obtained by dynamic viscoelasticity measurement, is preferably 10 to 30GPa at 50 ℃ and 1 to 10GPa at 120 ℃. In addition, the same applies to the piezoelectric layer 20.
Therefore, the storage modulus of the piezoelectric thin film 10 can have a large frequency dispersion under a high temperature environment exceeding 50 ℃. That is, the vibration damping material can exhibit rigidity against vibration of 20Hz to 20kHz, and exhibit flexibility against vibration of not more than logarithmic Hz.
Further, in the piezoelectric thin film 10, the product of the thickness and the storage modulus at a frequency of 1Hz obtained by dynamic viscoelasticity measurement is preferably 2.0X 10 at 50 DEG C5～5.0×106N/m, 1.0X 10 at 120 ℃5～2.0×106N/m. In addition, the same applies to the piezoelectric layer 20.
Therefore, the piezoelectric thin film 10 can have appropriate rigidity and mechanical strength in a range not impairing flexibility and acoustic characteristics in a high temperature environment exceeding 50 ℃.
Further, in the piezoelectric thin film 10, in the master curve obtained from the dynamic viscoelasticity measurement, the loss tangent at 25 ℃ and at a frequency of 1kHz is preferably 0.05 or more. In addition, the same applies to the piezoelectric layer 20.
Therefore, the frequency characteristics of the speaker using the piezoelectric film 10 become smooth, and the lowest resonance frequency f can be made0The change in sound quality when the change is accompanied by a change in curvature of the speaker is small.
In the present invention, the measurement of the storage modulus (young's modulus) and the loss tangent (dynamic viscoelasticity measurement) of the piezoelectric thin film 10, the piezoelectric layer 20, the laminated piezoelectric element 14, the vibration plate 12, and the like described later may be performed by a known method using a dynamic viscoelasticity measuring machine. As an example of the dynamic viscoelasticity measuring instrument, a DMS6100 viscoelasticity spectrometer manufactured by SII NanoTechnology inc.
As the measurement conditions, there can be exemplified a case where the measurement frequency is 0.1 to 20Hz (0.1Hz, 0.2Hz, 0.5Hz, 1Hz, 2Hz, 5Hz, 10Hz, and 20Hz), the measurement temperature is-50 to 170 ℃, the temperature rise rate is 2 ℃/min (in a nitrogen atmosphere), the sample size is 40mm x 10mm (including the jig region), and the chuck pitch is 20mm, respectively.
An example of the method for manufacturing the piezoelectric thin film 10 will be described below with reference to fig. 2 to 6.
First, as shown in fig. 2, a sheet 10a having a lower electrode 24 formed on a lower protective layer 28 is prepared. The sheet 10a may be produced by forming a thin copper film or the like as the lower electrode 24 on the surface of the lower protective layer 28 by vacuum deposition, sputtering, plating, or the like.
If necessary, the lower protective layer 28 with a separator (dummy support) may be used, for example, when the lower protective layer 28 is extremely thin and has poor handleability. Further, PET having a thickness of 25 to 100 μm or the like can be used as the separator. The separator may be removed after the upper electrode 26 and the upper protective layer 30 are thermocompression bonded, before any component is stacked on the lower protective layer 28.
In another aspect, the following coatings were prepared: the polymer material having viscoelasticity at normal temperature and the polymer material having viscoelasticity at high temperature are dissolved in an organic solvent, and the piezoelectric particles 36 such as PZT particles are added thereto and stirred and dispersed. In the following description, when it is not necessary to distinguish between a polymer material having viscoelasticity at normal temperature and a polymer material having viscoelasticity at high temperature, both are also collectively referred to as "viscoelasticity materials".
The organic solvent is not limited, and various organic solvents such as Dimethylformamide (DMF), methyl ethyl ketone, cyclohexanone, and the like can be used.
After preparing the sheet 10a and preparing the dope, the dope is cast (coated) on the sheet 10a, and the organic solvent is evaporated to be dried. Therefore, as shown in fig. 3, a laminate 10b is produced which has the lower electrode 24 on the lower protective layer 28 and the piezoelectric layer 20 formed on the lower electrode 24. The lower electrode 24 is an electrode on the substrate side when the piezoelectric layer 20 is applied, and does not indicate the positional relationship between the upper and lower sides of the laminate.
The method of casting the dope is not limited, and any known method (coating apparatus) such as a slide coater and a doctor blade can be used.
In addition, if the viscoelastic material is a material that can be heated and melted, such as cyanoethylated PVA, a melt can be prepared by heating and melting the viscoelastic material, and the piezoelectric particles 36 are added and dispersed thereto, and the melt can be sheet-extruded onto the sheet 10a shown in fig. 2 by extrusion molding or the like and cooled, so that a laminate 10b having the lower electrode 24 on the lower protective layer 28 and the piezoelectric layer 20 formed on the lower electrode 24 as shown in fig. 3 can be prepared.
As described above, in the piezoelectric film 10, a dielectric polymer material may be added to the substrate 34 in addition to the viscoelastic material such as cyanoethylated PVA.
When these polymer materials are added to the substrate 34, the polymer materials added to the coating material may be dissolved. Alternatively, the polymer material to be added may be added to the above-mentioned heat-fusible viscoelastic material and heated and fused.
After a laminate 10b having the lower electrode 24 on the lower protective layer 28 and the piezoelectric layer 20 formed on the lower electrode 24 is prepared, polarization treatment (poling) of the piezoelectric layer 20 is performed.
The method of polarization treatment of the piezoelectric layer 20 is not limited, and a known method can be used. As a preferable method of polarization treatment, the methods shown in fig. 4 and 5 can be exemplified.
In this method, as shown in fig. 4 and 5, a rod-like or wire-like corona electrode 40 movable along an upper surface 20a of a piezoelectric layer 20 of a laminate 10b is provided on the upper surface 20a at an interval g of, for example, 1 mm. The corona electrode 40 and the lower electrode 24 are then connected to a dc power supply 42.
Further, a heating mechanism, for example, a hot plate, for heating the holding laminated body 10b is prepared.
Then, the heating means applies a dc voltage of several kV, for example, 6kV, from the dc power supply 42 between the lower electrode 24 and the corona electrode 40 in a state where the piezoelectric layer 20 is heated and maintained at a temperature of 100 ℃. Further, while maintaining the gap g, the corona electrode 40 is moved (scanned) along the upper surface 20a of the piezoelectric layer 20 to perform polarization treatment of the piezoelectric layer 20.
Accordingly, the piezoelectric layer 20 is polarized in the thickness direction.
In the polarization treatment by the corona discharge, a known mechanism for moving the rod-like object may be used to move the corona electrode 40. In the following description, the polarization treatment by corona discharge will be also referred to as "corona polarization treatment" for convenience.
Also, in the corona polarization treatment, a method of moving the corona electrode 40 is not limited. That is, the corona electrode 40 may be fixed, a moving mechanism for moving the laminate 10b may be provided, and the laminate 10b may be moved to perform the polarization treatment. The stacked body 10b may be moved by a known sheet-like object moving mechanism.
Further, the number of corona electrodes 40 is not limited to 1, and a plurality of corona electrodes 40 may be used to perform corona polarization treatment.
The polarization treatment is not limited to the corona polarization treatment, and may be a normal electric field polarization in which a dc electric field is directly applied to an object to be subjected to the polarization treatment. In the case of performing the normal electric field polarization, the upper electrode 26 needs to be formed before the polarization treatment.
Before the polarization treatment, rolling treatment may be performed to smooth the surface of the piezoelectric layer 20 using a heating roller or the like. By performing this rolling treatment, the thermal compression bonding step described later can be smoothly performed.
While the piezoelectric layer 20 of the laminate 10b is polarized in this manner, the sheet 10c having the upper electrode 26 formed on the upper protective layer 30 is prepared. The sheet 10c may be produced by forming a copper thin film or the like as the upper electrode 26 on the surface of the upper protective layer 30 by vacuum deposition, sputtering, plating, or the like.
Next, as shown in fig. 6, the upper electrode 26 is directed to the piezoelectric layer 20, and the sheet 10c is laminated on the laminated body 10b in which the polarization process of the piezoelectric layer 20 is completed.
Further, the piezoelectric film 10 is produced by thermally pressing the laminate of the laminate 10b and the sheet 10c with a thermal press or a heating roller or the like so as to sandwich the upper protective layer 30 and the lower protective layer 28.
The laminated piezoelectric element 14 of the present invention described later has a structure in which the piezoelectric thin film 10 of the present invention is laminated and preferably bonded to the adhesive layer 19. In the laminated piezoelectric element 14 shown in fig. 8, preferably, the directions of polarization of the adjacent piezoelectric thin films 10 are opposite to each other as indicated by arrows marked on the piezoelectric layers 20.
In a typical multilayer ceramic piezoelectric element in which piezoelectric ceramics are laminated, a laminate of the piezoelectric ceramics is produced and then subjected to a polarization treatment. Only the common electrode exists at the interface of each piezoelectric layer, and therefore, the polarization directions of the piezoelectric layers alternate in the stacking direction.
In contrast, the piezoelectric thin film 10 constituting the laminated piezoelectric element of the present invention can be subjected to polarization treatment in the state of the piezoelectric thin film 10 before lamination. In the piezoelectric thin film 10, as shown in fig. 4 and 5, it is preferable that the polarization treatment of the piezoelectric layer 20 is performed by corona polarization treatment before the upper electrode 26 and the upper protective layer 30 are laminated.
Therefore, the laminated piezoelectric element of the present invention can be produced by laminating the piezoelectric thin films 10 subjected to polarization treatment. It is preferable that a long piezoelectric film (large-area piezoelectric film) subjected to polarization treatment is prepared and cut into individual piezoelectric films 10, and then the piezoelectric films 10 are laminated to form the laminated piezoelectric element 14.
Therefore, in the laminated piezoelectric element according to the present invention, as shown in fig. 10, the polarization directions in the adjacent piezoelectric thin films 10 can be aligned in the laminating direction as in the laminated piezoelectric element 61, and the polarization directions in the adjacent piezoelectric thin films 10 can be alternated as in the laminated piezoelectric element 14 shown in fig. 8.
Further, it is known that, in a general piezoelectric thin film made of a polymer material such as PVDF, molecular chains are oriented in the stretching direction by performing stretching treatment in a uniaxial direction after polarization treatment, and as a result, large piezoelectric characteristics are obtained in the stretching direction. Therefore, the piezoelectric thin film generally has in-plane anisotropy in piezoelectric characteristics, and has anisotropy in the amount of tension in the plane direction when a voltage is applied.
In contrast, the piezoelectric film 10 of the present invention, which is composed of a polymer composite piezoelectric body in which the piezoelectric particles 36 are dispersed in the matrix 34, can obtain a large piezoelectric characteristic without performing an extension treatment after the polarization treatment. Therefore, the piezoelectric thin film 10 of the present invention has no in-plane anisotropy in piezoelectric characteristics, and is isotropically stretched in all directions of the in-plane direction when a driving voltage is applied as described later.
The piezoelectric thin film 10 of the present invention can be produced using a sheet-like single sheet (cut sheet), and is preferably produced by Roll-to-Roll (Roll). In the following description, a roll-to-roll will also be referred to as "RtoR".
As is well known, RtoR is a manufacturing method in which a raw material is pulled out from a roll formed by winding a long raw material, conveyed in a longitudinal direction, subjected to various processes such as film formation and surface treatment, and wound into a roll again.
When the piezoelectric thin film 10 is manufactured by the above manufacturing method using RtoR, a 1 st roll in which the sheet 10a having the lower electrode 24 formed on the long lower protective layer 28 is wound and a 2 nd roll in which the sheet 10c having the upper electrode 26 formed on the long upper protective layer 30 is wound are used.
The 1 st and 2 nd volumes may be identical.
The sheet 10a is pulled out from the roll, conveyed in the longitudinal direction, coated with a coating material containing a viscoelastic material and piezoelectric particles 36, and dried by heating or the like to form the piezoelectric layer 20 on the lower electrode 24 as the laminate 10 b.
Next, the corona polarization is performed to perform polarization treatment of the piezoelectric layer 20. In the case of manufacturing the piezoelectric thin film 10 by RtoR, the laminate 10b is conveyed, and the polarization treatment of the piezoelectric layer 20 by corona polarization is performed by the long rod-shaped corona electrode 40 fixed in the direction orthogonal to the conveying direction of the laminate 10 b. The calendering treatment may be performed before the polarization treatment as described above.
Next, the sheet 10c is pulled out from the 2 nd roll, the sheet 10c and the laminate are conveyed, and the sheet 10c is laminated on the laminate 10b by a known method using a bonding roller or the like, with the upper electrode 26 facing the piezoelectric layer 20 as described above.
Thereafter, the laminated laminate 10b and the sheet 10c are thermally pressed by being sandwiched and conveyed by a heating roller pair, thereby completing the piezoelectric film 10 of the present invention, and the piezoelectric film 10 is wound into a roll shape.
In addition, the production environment of the piezoelectric thin film 10 is generally considered to be normal temperature. In contrast, as described above, the piezoelectric thin film 10 of the present invention has not only good flexibility in a high temperature region but also sufficient flexibility at normal temperature. Therefore, the piezoelectric thin film 10 of the present invention can also be suitably applied to a manufacturing method involving winding, such as RtoR.
In the above example, the piezoelectric thin film 10 of the present invention was produced by conveying the sheet (laminate) only 1 time in the longitudinal direction by RtoR, but the present invention is not limited to this.
For example, the laminate 10b is formed, subjected to corona polarization, and then wound into a roll. Next, the laminate may be pulled out from the laminate roll, transported in the longitudinal direction, and the piezoelectric thin film 10 may be completed by laminating the sheet having the upper electrode 26 formed on the upper protective layer 30 as described above, and the piezoelectric thin film 10 may be wound in a roll shape.
In such a piezoelectric thin film 10, when a voltage is applied to the lower electrode 24 and the upper electrode 26, the piezoelectric particles 36 are stretched in the polarization direction in accordance with the applied voltage. As a result, the piezoelectric thin film 10 (piezoelectric layer 20) contracts in the thickness direction. Meanwhile, the piezoelectric film 10 is also stretched in the in-plane direction due to the POISSON 'S RATIO (POISSON' S RATIO) relationship. The stretching is about 0.01 to 0.1%. The case of isotropic stretching in all directions of the in-plane direction is as described above.
As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the stretching in the thickness direction is very small, and the maximum is about 0.3 μm.
On the other hand, the piezoelectric thin film 10, that is, the piezoelectric layer 20 has a size much larger than the thickness in the plane direction. Therefore, for example, if the length of the piezoelectric film 10 is 20cm, the piezoelectric film 10 is stretched by about 0.2mm at most by application of voltage.
When pressure is applied to the piezoelectric thin film 10, electric power is generated by the action of the piezoelectric particles 36.
By utilizing this, the piezoelectric film 10 can be used for various applications such as a speaker, a microphone, and a pressure sensor as described above.
Fig. 7 is a conceptual diagram illustrating an example of a flat piezoelectric speaker using the piezoelectric thin film 10 according to the present invention.
The piezoelectric speaker 45 is a flat-type piezoelectric speaker using the piezoelectric thin film 10 of the present invention as a vibration plate for converting an electric signal into vibration energy. The piezoelectric speaker 45 can also be used as a microphone, a sensor, and the like.
The piezoelectric speaker 45 includes a piezoelectric film 10, a housing 43, a viscoelastic support 46, and a frame 48.
The housing 43 is a thin rectangular cylindrical housing formed of plastic or the like and having one open side.
The frame 48 is a plate having a through hole at the center and having the same shape as the upper end surface (open surface side) of the housing 43.
The viscoelastic support 46 has moderate viscosity and elasticity. The viscoelastic support 46 serves to efficiently convert the stretching motion of the piezoelectric film 10 into a back-and-forth motion (a motion in a direction perpendicular to the film surface) by supporting the piezoelectric film 10 and applying a certain mechanical bias to any portion of the piezoelectric film. Examples of the viscoelastic support 46 include wool felt, nonwoven fabric such as wool felt including rayon and PET, and glass wool.
The piezoelectric speaker 45 is configured such that a viscoelastic support 46 is housed in a case 43, the case 43 and the viscoelastic support 46 are covered with a piezoelectric film 10, and the frame 48 is fixed to the case 43 in a state where the periphery of the piezoelectric film 10 is pressed against the upper end surface of the case 43 by the frame 48.
In the piezoelectric speaker 45, the viscoelastic support 46 has a quadrangular prism shape whose height (thickness) is larger than the inner surface height of the housing 43.
Therefore, in the piezoelectric speaker 45, the viscoelastic support 46 is held in a state of being reduced in thickness by the piezoelectric thin film 10 being pressed downward in the peripheral portion of the viscoelastic support 46. Similarly, the curvature of the piezoelectric thin film 10 abruptly changes in the peripheral portion of the viscoelastic support 46, and a raised portion 45a that becomes lower toward the periphery of the viscoelastic support 46 is formed in the piezoelectric thin film 10. Further, the central region of the piezoelectric film 10 is pressed by the quadrangular prism-shaped viscoelastic support 46 to be (substantially) planar.
In the piezoelectric speaker 45, when the piezoelectric film 10 is stretched in the in-plane direction by application of the driving voltage to the lower electrode 24 and the upper electrode 26, the angle of the rising portion 45a of the piezoelectric film 10 changes by the action of the viscoelastic support 46 in order to absorb the amount of the stretching. As a result, the piezoelectric film 10 having a planar portion moves upward.
Conversely, when the piezoelectric thin film 10 contracts in the in-plane direction by application of the driving voltage to the lower electrode 24 and the upper electrode 26, the rising portion 45a of the piezoelectric thin film 10 changes its angle in the collapse direction (direction approaching the plane) in order to absorb the amount of contraction. As a result, the piezoelectric thin film 10 having a planar portion moves downward.
The piezoelectric speaker 45 generates sound by the vibration of the piezoelectric film 10.
In the piezoelectric thin film 10 of the present invention, the conversion from the stretching motion to the vibration can be achieved by keeping the piezoelectric thin film 10 in a state of being bent.
Therefore, the piezoelectric film 10 of the present invention can function as a speaker having flexibility by only holding the bent state without passing through the piezoelectric speaker 45.
An example of the electroacoustic transducer of the present invention is conceptually shown in fig. 8.
The electroacoustic transducer of the present invention has the laminated piezoelectric element or the piezoelectric film of the present invention and the vibration plate. In the laminated piezoelectric element of the present invention, the piezoelectric thin film of the present invention is laminated by 2 or more layers.
As described above, the piezoelectric thin film 10 of the present invention has excellent flexibility in a high temperature environment exceeding 50 ℃ and also has good flexibility in a normal temperature environment. Therefore, the laminated piezoelectric element of the present invention in which such piezoelectric thin films 10 are laminated has excellent flexibility even in a high-temperature environment exceeding 50 ℃ and also has good flexibility even in a normal-temperature environment.
Further, the electroacoustic transducer of the present invention preferably uses a diaphragm having flexibility. By using the vibrating plate having flexibility, the electroacoustic transducer of the present invention has excellent flexibility in a high-temperature environment exceeding 50 ℃ and also has good flexibility in a normal-temperature environment due to the action and effect of the laminated piezoelectric element.
An electroacoustic transducer 50 shown in fig. 8 has a laminated piezoelectric element 14 and a vibration plate 12. The laminated piezoelectric element 14 is a laminated piezoelectric element of the present invention. The laminated piezoelectric element 14 illustrated in the figure is formed by laminating 3 piezoelectric thin films 10 of the present invention described above.
In the electroacoustic transducer 50, the laminated piezoelectric element 14 and the vibrating plate 12 are bonded via the adhesive layer 16.
A power supply PS for applying a driving voltage is connected to the piezoelectric film 10 of the laminated piezoelectric element 14 constituting the electroacoustic transducer 50.
In fig. 8, the lower protective layer 28 and the upper protective layer 30 are omitted for simplicity of the drawing. In the laminated piezoelectric element 14 shown in fig. 8, however, all the piezoelectric thin films 10 preferably have both the lower protective layer 28 and the upper protective layer 30.
The laminated piezoelectric element of the present invention is not limited to this, and a piezoelectric film having a protective layer and a piezoelectric film having no protective layer may be present in combination. Further, when the piezoelectric film has a protective layer, the piezoelectric film may have only the lower protective layer 28 or only the upper protective layer 30. For example, in the case of the laminated piezoelectric element 14 having a 3-layer structure as shown in fig. 8, the following structure may be employed: in the figure, the uppermost piezoelectric film has only the upper protective layer 30, the piezoelectric film at the midpoint has no protective layer, and the lowermost piezoelectric film has only the lower protective layer 28.
In this regard, the same applies to the laminated piezoelectric element 56 shown in fig. 9 and the laminated piezoelectric element 61 shown in fig. 10, which will be described later.
In the following, in this type of electroacoustic transducer 50, a driving voltage is applied to the piezoelectric film 10 of the laminated piezoelectric element 14, whereby the piezoelectric film 10 is stretched in the planar direction, and the laminated piezoelectric element 14 is stretched in the planar direction by the stretching of the piezoelectric film 10.
The diaphragm 12 is bent by the tension in the plane direction of the laminated piezoelectric element 14, and as a result, the diaphragm 12 vibrates in the thickness direction. The vibration plate 12 generates sound by the vibration in the thickness direction. The vibrating plate 12 vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10, and generates a sound according to the driving voltage applied to the piezoelectric film 10.
That is, the electroacoustic transducer 50 is a speaker using the laminated piezoelectric element 14 of the present invention as an exciter.
In the electroacoustic transducer 50 of the present invention, the diaphragm 12 preferably has flexibility. In the present invention, the term "flexible" means that the sheet can be bent and rolled, specifically, can be bent and stretched without causing damage or injury, as is the same as the term for the general explanation.
The vibrating plate 12 preferably has flexibility, and various sheet-like objects (plate-like objects, thin films) can be used without limitation as long as they satisfy the relationship with the laminated piezoelectric element 14 described later.
Examples of the diaphragm 12 include a resin film made of polyethylene terephthalate (PET), polypropylene (PP), Polystyrene (PS), Polycarbonate (PC), Polyphenylene Sulfide (PPs), polymethyl methacrylate (PMMA), Polyetherimide (PEI), Polyimide (PI), polyethylene naphthalate (PEN), cellulose Triacetate (TAC), a cycloolefin resin, etc., a foamed plastic made of foamed polystyrene, foamed styrene, foamed polyethylene, etc., a sheet (veneer), a cork sheet, leather such as cow leather, etc., various paper boards such as carbon paper, japanese paper, etc., and various cardboard materials made by pasting other paper boards on one surface or both surfaces of a corrugated cardboard.
In the electroacoustic transducer 50 of the present invention, as long as the vibration plate 12 has flexibility, it is possible to preferably use a display device such as an organic Light Emitting diode (oled) display, a liquid crystal display, a micro-Light Emitting led (Light Emitting diode) display, or an inorganic electroluminescent display, or a screen for a projector.
In the electroacoustic transducer 50 of the illustrated example, the diaphragm 12 and the laminated piezoelectric element 14 are preferably bonded to each other through the adhesive layer 16.
In the present invention, as long as the vibration plate 12 and the laminated piezoelectric element 14 can be bonded to each other by the adhesive layer 16, various known adhesive layers can be used.
Therefore, the adhesive layer 16 may be a layer made of an adhesive which has fluidity at the time of bonding and then becomes solid, a layer made of an adhesive which is a soft solid in a gel state (rubber-like) at the time of bonding and then maintains the gel state, or a layer made of a material having characteristics of both the adhesive and the adhesive. The adhesive layer 16 may be formed by applying a flowable adhesive such as a liquid, or may be formed by using a sheet-like adhesive.
In the electroacoustic transducer 50 of the present invention, the laminated piezoelectric element 14 is stretched, and the diaphragm 12 is caused to vibrate in a bending manner, thereby generating sound. Therefore, in the electroacoustic transducer 50 of the present invention, it is preferable that the tension of the laminated piezoelectric element 14 is directly transmitted to the vibration plate 12. If a substance having viscosity such as relaxation of vibration exists between the vibrating plate 12 and the laminated piezoelectric element 14, the efficiency of transmitting the tensile energy of the laminated piezoelectric element 14 to the vibrating plate 12 decreases, and the driving efficiency of the electroacoustic transducer 50 decreases.
In view of this, the adhesive layer 16 is preferably an adhesive layer made of an adhesive which is a solid and can provide a hard adhesive layer 16, as compared with an adhesive layer made of an adhesive. More preferably, the adhesive layer 16 is an adhesive layer made of a thermoplastic adhesive such as a polyester adhesive and a styrene/butadiene rubber (SBR) adhesive.
Bonding is different from bonding and is useful when high bonding temperatures are required. The thermoplastic adhesive is preferable because it combines "relatively low temperature, short time and strong adhesion".
The thickness of the adhesive layer 16 is not limited, and may be set as appropriate so as to obtain a sufficient adhesive force (adhesive force ) depending on the material of the adhesive layer 16.
In the electroacoustic transducer 50 of the present invention, as the adhesive layer 16 becomes thinner, the effect of transmitting the tensile energy (vibration energy) to the laminated piezoelectric element 14 of the diaphragm 12 can be improved, and the energy efficiency can be improved. Further, if the adhesive layer 16 is thick and rigid, the extension of the laminated piezoelectric element 14 may be restricted.
In this regard, a thin adhesive layer 16 is preferred. Specifically, the thickness of the adhesive layer 16 is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and still more preferably 0.1 to 10 μm in terms of the thickness after adhesion.
In the electroacoustic transducer 50, the adhesive layer 16 is preferably provided, but is not an essential component.
Therefore, in the electroacoustic transducer 50, the diaphragm 12 and the laminated piezoelectric element 14 can be fixed by a known pressure bonding mechanism, a fastening mechanism, a fixing mechanism, and the like without the adhesive layer 16. For example, when the laminated piezoelectric element 14 has a rectangular shape, the electroacoustic transducer may be configured by fastening four corners with a member such as a nut (nut), or may be configured by fastening four corners with a central portion with a member such as a nut.
However, in this case, when the driving voltage is applied from the power supply PS, the laminated piezoelectric element 14 is stretched independently of the vibrating plate 12, and in some cases, the laminated piezoelectric element 14 is simply bent and the stretch of the laminated piezoelectric element 14 is not transmitted to the vibrating plate 12. As described above, when the laminated piezoelectric element 14 is stretched independently of the vibrating plate 12, the vibration efficiency of the vibrating plate 12 by the laminated piezoelectric element 14 may be reduced, and the vibrating plate 12 may not be sufficiently vibrated.
In view of this, in the electroacoustic transducer of the present invention, the vibrating plate 12 and the laminated piezoelectric element 14 are preferably bonded to each other by the adhesive layer 16 as illustrated in the figure.
In the electroacoustic transducer 50 shown in fig. 8, the laminated piezoelectric element 14 has a structure in which 3 piezoelectric films 10 are laminated and adjacent piezoelectric films 10 are bonded via the adhesive layer 19. A power supply PS for applying a driving voltage for stretching the piezoelectric film 10 is connected to each piezoelectric film 10.
The laminated piezoelectric element 14 shown in fig. 8 is a laminate of 3 piezoelectric thin films 10, but the present invention is not limited thereto. That is, in the laminated piezoelectric element of the present invention, the number of laminated piezoelectric thin films 10 may be 2 or 4 or more, as long as the piezoelectric thin films 10 are laminated by 2 or more. In this regard, the same applies to the laminated piezoelectric element 56 shown in fig. 9 and the laminated piezoelectric element 61 shown in fig. 10, which will be described later.
In the electroacoustic transducer of the present invention, the piezoelectric film of the present invention may be used instead of the laminated piezoelectric element 14 of the present invention, and the diaphragm 12 may be vibrated to generate sound with the same operational effect. That is, the electroacoustic transducer of the present invention can use the piezoelectric film of the present invention as an exciter.
Preferably, the laminated piezoelectric element 14 shown in fig. 8 has the following structure: the polarization directions of the adjacent piezoelectric films 10 are set to be opposite to each other, 2 or more (3 layers in the example of the figure) piezoelectric films 10 are laminated, and the adjacent piezoelectric films 10 are bonded by the adhesive layer 19.
In the present invention, as long as the adhesive layer 19 can adhere the adjacent piezoelectric films 10, various known adhesive layers can be used.
Therefore, the adhesive layer 19 may be a layer composed of the adhesive, a layer composed of an adhesive, or a layer composed of a material having both the characteristics of the adhesive and the adhesive. The adhesive layer 19 may be formed by applying a flowable adhesive such as a liquid, or may be formed by using a sheet-like adhesive.
The laminated piezoelectric element 14 generates sound by stretching the laminated piezoelectric films 10 and vibrating the diaphragm 12. Therefore, in the laminated piezoelectric element 14, the tension of each piezoelectric film 10 is preferably directly transmitted. If a substance having viscosity such as relaxation of vibration exists between the piezoelectric thin films 10, the transmission efficiency of the tensile energy of the piezoelectric thin films 10 decreases, and the driving efficiency of the laminated piezoelectric element 14 decreases.
In view of this, the adhesive layer 19 is preferably an adhesive layer made of an adhesive which is a solid and can provide a hard adhesive layer 19, as compared with an adhesive layer made of an adhesive. More preferably, the adhesive layer 19 is made of a thermoplastic adhesive such as a polyester adhesive and a styrene/butadiene rubber (SBR) adhesive.
Bonding is different from bonding and is useful when high bonding temperatures are required. The thermoplastic adhesive is preferable because it combines "relatively low temperature, short time and strong adhesion".
In the laminated piezoelectric element 14, the thickness of the adhesive layer 19 is not limited, and a thickness that exhibits a sufficient adhesive force may be appropriately set according to the material for forming the adhesive layer 19.
In the laminated piezoelectric element 14 illustrated in the figure, as the adhesive layer 19 becomes thinner, the effect of transmitting the tensile energy of the piezoelectric film 10 can be improved, and the energy efficiency can be improved. Further, if the adhesive layer 19 is thick and rigid, the stretching of the piezoelectric film 10 may be restricted.
In view of this, the adhesive layer 19 is preferably thinner than the piezoelectric layer 20. That is, in the laminated piezoelectric element 14, the adhesive layer 19 is preferably hard and thin. Specifically, the thickness of the adhesive layer 19 is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and still more preferably 0.1 to 10 μm in terms of the thickness after adhesion.
As will be described later, in the laminated piezoelectric element 14 of the illustrated example, the polarization directions of the adjacent piezoelectric films are opposite to each other, and the adhesive layer 19 can be made thin because there is no short circuit between the adjacent piezoelectric films 10.
In the laminated piezoelectric element 14 of the illustrated example, if the spring constant (thickness × young's modulus) of the adhesive layer 19 is high, there is a possibility that the extension of the piezoelectric film 10 is limited. Therefore, the spring constant of the adhesive layer 19 is preferably equal to or less than the spring constant of the piezoelectric film 10.
Specifically, the product of the thickness of the adhesive layer 19 and the storage modulus (E') at a frequency of 1Hz as measured by dynamic viscoelasticity is preferably 2.0X 10 at 0 DEG C6N/m or less, 1.0X 10 at 50 DEG C6N/m or less.
Further, it is preferable that the internal loss of the adhesive layer at a frequency of 1Hz, which is obtained by dynamic viscoelasticity measurement, is 1.0 or less at 25 ℃ in the case of the adhesive layer 19 made of an adhesive, and is 0.1 or less at 25 ℃ in the case of the adhesive layer 19 made of an adhesive.
In the laminated piezoelectric element 14 constituting the electroacoustic transducer 50, the adhesive layer 19 is preferably provided, but is not an essential component.
Therefore, the laminated piezoelectric element constituting the electroacoustic transducer of the present invention may be configured by laminating and adhering the piezoelectric film 10 by a known pressure bonding mechanism, fastening mechanism, fixing mechanism, or the like without the adhesive layer 19. For example, when the piezoelectric film 10 is rectangular, the laminated piezoelectric element may be configured by fastening four corners with nuts or the like, or by fastening four corners with a central portion with nuts or the like. Alternatively, the laminated piezoelectric element may be configured by laminating the piezoelectric thin films 10 and then attaching an adhesive tape to the peripheral portion (end face) to fix the laminated piezoelectric thin films 10.
However, in this case, when a driving voltage is applied from the power supply PS, the piezoelectric films 10 are stretched independently, and in some cases, the respective piezoelectric films 10 are bent in opposite directions to form gaps. When the piezoelectric thin films 10 are independently stretched in this manner, the driving efficiency of the laminated piezoelectric element is reduced, and the stretching of the entire laminated piezoelectric element is reduced, which may cause insufficient vibration of the vibrating plate or the like in contact therewith. In particular, when the respective piezoelectric thin films 10 are bent in opposite directions to generate gaps, the driving efficiency as a laminated piezoelectric element is significantly reduced.
In view of this, as in the laminated piezoelectric element 14 illustrated in the figure, the laminated piezoelectric element of the present invention preferably has an adhesive layer 19 for adhering the adjacent piezoelectric films 10 to each other.
As shown in fig. 8, in the electroacoustic transducer 50, a power supply PS for supplying driving power, which is a driving voltage for stretching the piezoelectric film 10, is connected to the lower electrode 24 and the upper electrode 26 of each piezoelectric film 10.
The power supply PS is not limited, and may be a dc power supply or an ac power supply. The driving voltage may be appropriately set according to the thickness, the material, and the like of the piezoelectric layer 20 of each piezoelectric thin film 10, so that each piezoelectric thin film 10 can be appropriately driven.
As will be described later, in the laminated piezoelectric element 14 of the illustrated example, the polarization directions of the adjacent piezoelectric thin films 10 are opposite to each other. Therefore, in the adjacent piezoelectric thin films 10, the lower electrodes 24 and the upper electrodes 26 face each other. Therefore, regardless of the ac power supply or the dc power supply, the power supply PS always supplies power of the same polarity to the opposite electrodes. For example, in the laminated piezoelectric element 14 shown in fig. 8, power of the same polarity is always supplied to the upper electrode 26 of the piezoelectric film 10 at the lowermost layer in the figure and the upper electrode 26 of the piezoelectric film 10 at the 2 nd layer (the midpoint) and power of the same polarity is always supplied to the lower electrode 24 of the piezoelectric film 10 at the 2 nd layer and the lower electrode 24 of the piezoelectric film 10 at the uppermost layer in the figure.
The method of extracting the electrodes from the lower electrode 24 and the upper electrode 26 is not limited, and various known methods can be used.
As an example, a method of connecting a conductor such as a copper foil to the lower electrode 24 and the upper electrode 26 to lead out an electrode to the outside, a method of forming a through hole in the lower protective layer 28 and the upper protective layer 30 by laser or the like, and filling a conductive material in the through hole to lead out an electrode to the outside, and the like can be given.
Examples of a preferable electrode lead-out method include the method described in japanese patent application laid-open No. 2014-209724 and the method described in japanese patent application laid-open No. 2016-015354.
As described above, the piezoelectric layer 20 is formed by dispersing the piezoelectric particles 36 in the matrix 34. Further, the lower electrode 24 and the upper electrode 26 are provided so as to sandwich the piezoelectric layer 20 in the thickness direction.
When a voltage is applied to the lower electrode 24 and the upper electrode 26 of the piezoelectric thin film 10 having such a piezoelectric layer 20, the piezoelectric particles 36 are stretched in the polarization direction in accordance with the applied voltage. As a result, the piezoelectric thin film 10 (piezoelectric layer 20) contracts in the thickness direction. Meanwhile, the piezoelectric film 10 is also stretched in the in-plane direction due to the POISSON 'S RATIO (POISSON' S RATIO) relationship.
The stretching is about 0.01 to 0.1%.
As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the stretching in the thickness direction is very small, and the maximum is about 0.3 μm.
On the other hand, the piezoelectric thin film 10, that is, the piezoelectric layer 20 has a size much larger than the thickness in the plane direction. Therefore, for example, if the length of the piezoelectric film 10 is 20cm, the piezoelectric film 10 is stretched by about 0.2mm at most by application of voltage.
The laminated piezoelectric element 14 is formed by laminating and bonding the piezoelectric thin films 10. Therefore, when the piezoelectric film 10 is stretched, the laminated piezoelectric element 14 is also stretched.
The vibrating plate 12 is bonded to the laminated piezoelectric element 14 via the adhesive layer 16. Therefore, the diaphragm 12 is bent by the extension of the laminated piezoelectric element 14, and as a result, the diaphragm 12 vibrates in the thickness direction.
The vibration plate 12 generates sound by the vibration in the thickness direction. That is, the vibrating plate 12 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 10, and generates a sound according to the driving voltage applied to the piezoelectric film 10.
As described above, a general piezoelectric thin film made of a polymer material such as PVDF has in-plane anisotropy in piezoelectric properties, and has anisotropy in the amount of tension in the plane direction when a voltage is applied.
In contrast, in the electroacoustic transducer 50 of the illustrated example, the piezoelectric film 10 of the present invention constituting the laminated piezoelectric element 14 has no in-plane anisotropy in piezoelectric characteristics and is isotropically stretched in all directions of the in-plane direction. That is, in the electroacoustic transducer 50 of the illustrated example, the piezoelectric film 10 constituting the laminated piezoelectric element 14 is isotropically stretched in two dimensions.
By laminating the laminated piezoelectric element 14 in which such piezoelectric films 10 that are isotropically stretched two-dimensionally are laminated, the vibrating plate 12 can be vibrated with a large force, and thus a larger and more beautiful sound can be generated, as compared with a case where general piezoelectric films such as PVDF that are stretched greatly in only one direction are laminated.
The laminated piezoelectric element 14 illustrated in the figure is formed by laminating a plurality of piezoelectric thin films 10. In the laminated piezoelectric element 14 of the illustrated example, adjacent piezoelectric films 10 are preferably bonded to each other by the adhesive layer 19.
Therefore, even if the rigidity per 1 piezoelectric film 10 is low and the tensile force is small, the rigidity is increased by laminating the piezoelectric films 10, and the tensile force as the laminated piezoelectric element 14 is increased. As a result, in the laminated piezoelectric element 14, even if the diaphragm 12 has a certain degree of rigidity, the diaphragm 12 can be sufficiently bent with a large force, and the diaphragm 12 can be sufficiently vibrated in the thickness direction to generate a sound in the diaphragm 12.
Further, the thicker the piezoelectric layer 20 is, the greater the tensile force of the piezoelectric thin film 10 is, but the driving voltage required to stretch the same amount increases by that amount. As described above, in the laminated piezoelectric element 14, the thickness of the piezoelectric layer 20 is preferably about 300 μm at the maximum. Therefore, even if the voltage applied to each piezoelectric film 10 is small, the piezoelectric film 10 can be sufficiently stretched.
In the electroacoustic transducer 50 of the present invention, the product of the thickness of the laminated piezoelectric element 14 and the storage modulus of the laminated piezoelectric element 14 at 25 ℃ at a frequency of 1Hz as measured by dynamic viscoelasticity is preferably 0.1 to 3 times the product of the thickness of the vibration plate 12 and the young's modulus.
As described above, the piezoelectric thin film 10 of the present invention has good flexibility, and particularly has excellent flexibility in a high-temperature environment of 50 ℃ or higher, and the laminated piezoelectric element 14 of the present invention in which the piezoelectric thin film 10 is laminated also has good flexibility, and particularly has excellent flexibility in a high-temperature environment of 50 ℃ or higher.
On the other hand, the vibration plate 12 has a certain degree of rigidity. When such a diaphragm 12 is combined with the laminated piezoelectric element 14 having high rigidity, the diaphragm is hard and not easily bent, which is disadvantageous in terms of flexibility of the electroacoustic transducer 50.
In contrast, in the electroacoustic transducer 50 of the present invention, the product of the thickness of the laminated piezoelectric element 14 and the storage modulus at a frequency of 1Hz and 25 ℃ obtained by dynamic viscoelasticity measurement is preferably 3 times or less the product of the thickness of the vibration plate 12 and the young's modulus. That is, the spring constant of the laminated piezoelectric element 14 is preferably 3 times or less the diaphragm 12 with respect to a slow operation.
With such a configuration, the electroacoustic transducer 50 of the present invention can exhibit flexibility for a slow motion due to an external force such as bending and rolling, that is, can exhibit excellent flexibility for a slow motion.
In the electroacoustic transducer 50 of the present invention, the product of the thickness of the laminated piezoelectric element 14 and the storage modulus at a frequency of 1Hz and 25 ℃ obtained by dynamic viscoelasticity measurement is more preferably 2 times or less, still more preferably 1 time or less, and particularly preferably 0.3 time or less, the product of the thickness of the vibration plate 12 and the young's modulus.
On the other hand, considering the material used for the laminated piezoelectric element 14, the preferable structure of the laminated piezoelectric element 14, and the like, the product of the thickness of the laminated piezoelectric element 14 and the storage modulus at a frequency of 1Hz and 25 ℃ obtained by dynamic viscoelasticity measurement is preferably 0.1 times or more the product of the thickness of the vibrating plate 12 and the young's modulus.
In the electroacoustic transducer 50 of the present invention, it is preferable that the product of the thickness of the laminated piezoelectric element 14 and the storage modulus of the laminated piezoelectric element 14 at 25 ℃ at a frequency of 1kHz on the main curve obtained by the dynamic viscoelasticity measurement is 0.3 to 10 times the product of the thickness of the vibration plate 12 and the young's modulus. That is, in the fast operation in the driven state, the spring constant of the laminated piezoelectric element 14 is preferably 0.3 to 10 times that of the vibrating plate 12.
As described above, the electroacoustic transducer 50 generates sound by vibrating the vibration plate 12 by the tension in the plane direction of the laminated piezoelectric element 14. Therefore, the laminated piezoelectric element 14 preferably has a certain degree of rigidity (hardness, toughness) with respect to the vibration plate 12 in the audio band at frequencies (20Hz to 20 kHz).
In the electroacoustic transducer 50 of the present invention, the product of the thickness of the laminated piezoelectric element 14 and the storage modulus at 25 ℃ at a frequency of 1kHz on the principal curve obtained by the dynamic viscoelasticity measurement is preferably 0.3 times or more, more preferably 0.5 times or more, and still more preferably 1 time or more the product of the thickness of the diaphragm 12 and the young's modulus. That is, the spring constant of the laminated piezoelectric element 14 is preferably 0.3 times or more, more preferably 0.5 times or more, and further preferably 1 time or more the diaphragm 12, relative to the snap action.
Therefore, at the frequencies of the audio band, the rigidity of the laminated piezoelectric element 14 with respect to the vibration plate 12 is sufficiently ensured, and therefore the electroacoustic transducer 50 can output a sound of a high sound pressure with high energy efficiency.
On the other hand, considering the material used for the laminated piezoelectric element 14, the preferable structure of the laminated piezoelectric element 14, and the like, the product of the thickness of the laminated piezoelectric element 14 and the storage modulus at a frequency of 1kHz and 25 ℃ obtained by dynamic viscoelasticity measurement is preferably 10 times or less the product of the thickness of the vibration plate 12 and the young's modulus.
As is apparent from the above description, not only the thickness of the adhesive layer 19 but also the physical properties such as the storage modulus of the adhesive layer 19 greatly affect the product of the thickness of the actuator 14 and the storage modulus at 25 ℃ at a frequency of 1Hz, which is obtained by the dynamic viscoelasticity measurement.
On the other hand, not only the thickness of the vibrating plate but also the physical properties of the vibrating plate greatly affect the product of the thickness of the vibrating plate 12 and the young's modulus.
Therefore, in the electroacoustic transducer 50 of the present invention, in order to satisfy the condition that the product of the thickness of the laminated piezoelectric element 14 and the storage modulus of the laminated piezoelectric element 14 at a frequency of 1Hz and 25 ℃ obtained by dynamic viscoelasticity measurement is 0.1 to 3 times the product of the thickness of the vibrating plate 12 and the young's modulus, the thickness and material of the adhesive layer 19, and the thickness and material of the vibrating plate are important. In the electroacoustic transducer 50 of the present invention, in order to satisfy the condition that the product of the thickness of the laminated piezoelectric element 14 and the storage modulus of the laminated piezoelectric element 14 at a frequency of 1kHz and 25 ℃ is 0.3 to 10 times the product of the thickness of the vibrating plate 12 and the young's modulus, the thickness and material of the adhesive layer 19, and the thickness and material of the vibrating plate are also important.
That is, in the electroacoustic transducer 50 of the present invention, in order to satisfy the above-described conditions, it is preferable to appropriately select the thickness and material of the adhesive layer 19 and the thickness and material of the diaphragm 12.
In other words, in the electroacoustic transducer 50 of the present invention, the thickness and material of the adhesive layer 19, and the thickness and material of the vibrating plate 12 are appropriately selected in accordance with the characteristics of the piezoelectric film 18, and the like, and therefore, it is possible to preferably satisfy the condition that the product of the thickness of the laminated piezoelectric element 14 and the storage modulus of the laminated piezoelectric element 14 at a frequency of 1Hz and 25 ℃ obtained by dynamic viscoelasticity measurement is 0.1 to 3 times the product of the thickness and young's modulus of the vibrating plate 12, and/or the condition that the product of the thickness of the laminated piezoelectric element 14 and the storage modulus of the laminated piezoelectric element 14 at a frequency of 1kHz and 25 ℃ is 0.3 to 10 times the product of the thickness and young's modulus of the vibrating plate 12.
The same applies to the case where the piezoelectric thin film 10 is used instead of the laminated piezoelectric element 14 to construct the electroacoustic transducer, regarding the product of the thickness and the storage modulus.
In the electroacoustic transducer 50 of the illustrated example, as described above, the polarization directions of the piezoelectric layers 20 of the adjacent piezoelectric films 10 of the laminated piezoelectric element 14 are preferably opposite to each other.
In the piezoelectric thin film 10, the polarity of the voltage applied to the piezoelectric layer 20 depends on the polarization direction. Therefore, regarding the polarity of the applied voltage, in the polarization direction shown by the arrow in fig. 8, the polarity of the electrode on the side of the direction indicated by the arrow (the downstream side of the arrow) and the polarity of the electrode on the opposite side (the upstream side of the arrow) are the same in all the piezoelectric thin films 10.
In the illustrated example, the lower electrode 24 is an electrode on the side of the direction indicated by the arrow indicating the polarization direction, the upper electrode 26 is an electrode on the opposite side, and the polarities of the upper electrode 26 and the lower electrode 24 are the same in all the piezoelectric thin films 10.
Therefore, in the laminated piezoelectric element 14 in which the polarization directions of the piezoelectric layers 20 of the adjacent piezoelectric films 10 are opposite to each other, the upper electrodes 26 face each other on one surface and the lower electrodes face each other on the other surface of the adjacent piezoelectric films 10. Therefore, in the laminated piezoelectric element 14, even if the electrodes of the adjacent piezoelectric thin films 10 are in contact with each other, short circuits (short) are unlikely to occur.
As described above, in order to stretch the laminated piezoelectric element 14 with good energy efficiency, the adhesive layer 19 is preferably made thin so that the adhesive layer 19 does not inhibit the stretching of the piezoelectric layer 20.
In contrast, in the laminated piezoelectric element 14 of the illustrated example in which short-circuiting is unlikely to occur even when the electrodes of the adjacent piezoelectric films 10 are in contact with each other, the adhesive layer 19 may not be provided, and even when the adhesive layer 19 is provided as a preferable aspect, the adhesive layer 19 can be made extremely thin as long as a required adhesive force can be obtained.
Therefore, the laminated piezoelectric element 14 can be stretched with high energy efficiency.
As described above, in the piezoelectric thin film 10, the absolute amount of the tension of the piezoelectric layer 20 in the thickness direction is very small, and the tension of the piezoelectric thin film 10 is substantially present only in the plane direction.
Therefore, even if the polarization directions of the laminated piezoelectric films 10 are opposite, all the piezoelectric films 10 are stretched in the same direction as long as the polarities of the voltages applied to the lower electrodes 24 and the upper electrodes 26 are correct.
In the laminated piezoelectric element 14, the polarization direction of the piezoelectric thin film 10 may be detected by a d33 detector or the like.
Alternatively, the polarization direction of the piezoelectric film 10 may be known from the processing conditions of the corona polarization treatment described above.
In the laminated piezoelectric element 14 of the illustrated example, it is preferable to form a long (large-area) piezoelectric film as described above and cut the long piezoelectric film to form individual piezoelectric films 10. Therefore, in this case, all of the plurality of piezoelectric thin films 10 constituting the laminated piezoelectric element 14 may be the same.
However, the present invention is not limited thereto. That is, in the electroacoustic transducer of the present invention, the piezoelectric laminate can have various structures such as a structure in which a piezoelectric film having the lower protective layer 28 and the upper protective layer 30 is laminated with a piezoelectric film having a different layer structure such as a piezoelectric film having no lower protective layer 28 and no upper protective layer 30, and a structure in which a piezoelectric film having a different thickness of the piezoelectric layer 20 is laminated.
In the child electroacoustic transducer 50 shown in fig. 8, the laminated piezoelectric element 14 is formed by laminating a plurality of piezoelectric films 10 so that the polarization directions of the adjacent piezoelectric films are opposite to each other, and the adjacent piezoelectric films 10 are preferably bonded by the adhesive layer 19.
The laminated piezoelectric element of the present invention is not limited to this, and various structures can be used.
Fig. 9 shows an example thereof. In the laminated piezoelectric element 56 shown in fig. 9, since a plurality of members similar to those of the laminated piezoelectric element 14 are used, the same members are denoted by the same reference numerals, and different portions will be mainly described.
The laminated piezoelectric element 56 shown in fig. 9 is a more preferable embodiment of the laminated piezoelectric element of the present invention, and the piezoelectric thin film 10L is laminated by 2 or more layers by folding the long piezoelectric thin film 10L in the longitudinal direction 1 or more times (preferably, a plurality of times). In addition, similarly to the laminated piezoelectric element 14 shown in fig. 8 and the like, the laminated piezoelectric element 56 shown in fig. 9 is also preferably formed by bonding the piezoelectric film 10L laminated by folding with the adhesive layer 19.
By folding and laminating 1 long piezoelectric film 10L polarized in the thickness direction, the polarization direction of the piezoelectric films 10L adjacent (opposing) in the lamination direction is reversed as shown by the arrow in fig. 9. In addition, the folding of the piezoelectric film may be in the short side direction rather than the long side direction.
According to this configuration, the laminated piezoelectric element 56 can be configured by only 1 long piezoelectric thin film 10L, and the number of power sources PS for applying the driving voltage is only 1, and furthermore, the extraction of the electrode from the piezoelectric thin film 10L can be 1.
Therefore, the laminated piezoelectric element 56 shown in fig. 9 can reduce the number of parts, simplify the structure, improve the reliability as a piezoelectric element (module), and reduce the cost.
As the laminated piezoelectric element 56 shown in fig. 9, in the laminated piezoelectric element 56 obtained by folding the long piezoelectric thin film 10L, it is preferable to insert the core rod 58 in the folded portion of the piezoelectric thin film 10L so as to be in contact with the piezoelectric thin film 10L.
As described above, the lower electrode 24 and the upper electrode 26 of the piezoelectric thin film 10L are formed of a deposited film of metal or the like. When the metal deposition film is bent at an acute angle, cracks (cracks) and the like are likely to occur, and thus, the electrode may be broken. That is, in the laminated piezoelectric element 56 shown in fig. 9, cracks and the like are likely to occur in the electrodes on the inner side of the bent portion.
In contrast, in the laminated piezoelectric element 56 in which the long piezoelectric thin film 10L is folded, the lower electrode 24 and the upper electrode 26 are prevented from being bent by inserting the core rod 58 into the folded portion of the piezoelectric thin film 10L, and thus, it is preferable to prevent the occurrence of disconnection.
In the electroacoustic transducer of the present invention, the adhesive layer 19 having conductivity may be used for laminating the piezoelectric element. In particular, in the laminated piezoelectric element 56 in which 1 long piezoelectric film 10L as shown in fig. 9 is laminated by being folded, the adhesive layer 19 having conductivity can be preferably used.
In the laminated piezoelectric element in which the polarization directions of the adjacent piezoelectric thin films 10 are opposite to each other as shown in fig. 8 and 9, the same polarity of electric power is supplied to the opposing electrodes in the laminated piezoelectric thin films 10. Therefore, a short circuit does not occur between the opposing electrodes.
On the other hand, in the laminated piezoelectric element 56 in which the piezoelectric thin film 10L is folded and laminated as described above, disconnection of the electrodes is likely to occur inside the bent portion folded at an acute angle.
Therefore, by sticking the laminated piezoelectric thin film 10L to the adhesive layer 19 having conductivity, even if disconnection of the electrode occurs inside the bent portion, conduction can be secured by the adhesive layer 19, and therefore disconnection can be prevented and reliability of the laminated piezoelectric element 56 can be greatly improved.
As shown in fig. 1, the piezoelectric thin film 10L constituting the laminated piezoelectric element 56 preferably includes a lower protective layer 28 and an upper protective layer 30 so as to face the lower electrode 24 and the upper electrode 26 with the laminate interposed therebetween.
In this case, even if the adhesive layer 19 having conductivity is used, the conductivity cannot be secured. Therefore, when the piezoelectric film 10L has the protective layer, the lower electrode 24 and the upper electrode 26 may be brought into contact with the adhesive layer 19 having conductivity by providing through holes in the lower protective layer 28 and the upper protective layer 30 in regions where the lower electrodes 24 and the upper electrodes 26 of the laminated piezoelectric film 10L face each other. It is preferable that the through holes formed in the lower protective layer 28 and the upper protective layer 30 are closed with a silver paste or a conductive adhesive, and then the adjacent piezoelectric thin films 10L are bonded through the conductive adhesive layer 19.
The through-holes of the lower protective layer 28 and the upper protective layer 30 may be formed by laser processing, removal of the protective layers by solvent etching, mechanical polishing, or the like.
The through-holes of the lower protective layer 28 and the upper protective layer 30 may be 1 or more in the region where the lower electrodes 24 and the upper electrodes 26 of the laminated piezoelectric thin film 10L face each other, except for the bent portion of the piezoelectric thin film 10L. Alternatively, the through holes of the lower protective layer 28 and the upper protective layer 30 may be formed regularly or irregularly over the entire surfaces of the lower protective layer 28 and the upper protective layer 30.
The conductive adhesive layer 19 is not limited, and various known conductive adhesive layers can be used.
In the laminated piezoelectric element described above, the polarization directions of the laminated piezoelectric thin films 10 are opposite in the adjacent piezoelectric thin films 10, but the present invention is not limited thereto.
That is, in the present invention, the laminated piezoelectric element in which the piezoelectric thin films 10 are laminated may be a laminated piezoelectric element 61 as shown in fig. 10, and all the polarization directions of the piezoelectric layers 20 may be the same direction.
However, as shown in fig. 10, in the laminated piezoelectric element 61 in which the polarization directions of the piezoelectric thin films 10 to be laminated are all the same, the lower electrode 24 and the upper electrode 26 face each other in the adjacent piezoelectric thin films 10. Therefore, if the adhesive layer 19 is not sufficiently thick, the lower electrode 24 and the upper electrode 26 of the adjacent piezoelectric thin films 10 may contact each other at the outer end portion in the surface direction of the adhesive layer 19, which may cause a short circuit.
Therefore, as shown in fig. 10, in the laminated piezoelectric element 61 in which all the polarization directions of the piezoelectric thin films 10 to be laminated are the same, the adhesive layer 19 cannot be made thin, which is disadvantageous in energy efficiency compared to the laminated piezoelectric elements shown in fig. 8 and 9.
However, as shown in fig. 9, a laminated piezoelectric element in which a plurality of piezoelectric films are laminated by folding 1 piezoelectric film can be considered in 2 structures.
The 1 st structure is a structure in which a bent portion based on folding of a piezoelectric film is along the longitudinal direction of a laminated piezoelectric element. That is, the 1 st structure is a structure in which the bending portion by folding of the piezoelectric film coincides with the longitudinal direction of the laminated piezoelectric element.
The 2 nd structure is a structure in which a bent portion based on folding of the piezoelectric film is in the short side direction of the laminated piezoelectric element. That is, the 2 nd structure is a structure in which the bending portion by folding of the piezoelectric film coincides with the short side direction of the laminated piezoelectric element.
In other words, regarding the laminated piezoelectric element in which the piezoelectric thin films are folded and laminated, a structure in which the ridge line formed by folding the piezoelectric thin films coincides with the longitudinal direction of the laminated piezoelectric element and a structure in which the ridge line coincides with the short-side direction of the laminated piezoelectric element can be considered.
Specifically, the longitudinal direction and the short-side direction of the laminated piezoelectric element are the longitudinal direction and the short-side direction in a planar shape when the laminated piezoelectric element is viewed in the lamination direction of the piezoelectric thin films 12.
In other words, the planar shape when the laminated piezoelectric element is viewed in the lamination direction of the piezoelectric thin films 12 is a shape when the laminated piezoelectric element is viewed from a direction orthogonal to the main surfaces of the piezoelectric thin films 12.
Specifically, since 1 piezoelectric film is folded and 5 laminated piezoelectric films are laminated, the following 2 structures can be considered when a 20 × 5cm laminated piezoelectric device is manufactured.
As conceptually shown in fig. 11, the 1 st structure is a laminated piezoelectric element 56A in which a rectangular piezoelectric film 10La of 20 × 25cm is folded 4 times in a direction of 25cm for 5cm each time to laminate 5 the piezoelectric films 10 La. In the laminated piezoelectric element 56A, a bent portion by folding of the piezoelectric film 10La is along the longitudinal direction of the laminated piezoelectric element 56A, that is, the direction of 20 cm. That is, in the laminated piezoelectric element 56A, the ridge line formed by folding the piezoelectric film 10La coincides with the longitudinal direction of the laminated piezoelectric element 56A.
As conceptually shown in fig. 12, the 2 nd structure is a laminated piezoelectric element 56B in which a rectangular piezoelectric film 10Lb of 100 × 5cm is folded 4 times by 20cm in the direction of 100cm to laminate 5 the piezoelectric films 10 Lb. In the laminated piezoelectric element 56B, a bent portion resulting from folding of the piezoelectric film 10Lb is along the longitudinal direction of the laminated piezoelectric element 56B, that is, the direction of 5 cm. That is, in the laminated piezoelectric element 56B, the ridge line formed by folding the piezoelectric film 10Lb coincides with the short side direction of the laminated piezoelectric element 56B.
In the present invention, the laminated piezoelectric element in which the piezoelectric thin films are folded and laminated can preferably use either a structure in which a bending portion by folding of the piezoelectric thin films is along the longitudinal direction of the laminated piezoelectric element or a structure in which the bending portion is along the short-side direction of the laminated piezoelectric element.
That is, the structure in which the bending portion by the folding of the piezoelectric film is along the longitudinal direction of the laminated piezoelectric element and the structure in the short-side direction have advantages, respectively. Therefore, any configuration may be used, as appropriate, depending on the application of the laminated piezoelectric element, and the like.
In the laminated piezoelectric element, a lead line may be provided to be connected to the lower electrode 24 and the upper electrode 26 and to reach the outside of the laminated piezoelectric element in order to connect to an external device such as a power supply device. The lead line does not necessarily physically protrude to the outside, and indicates an electrical lead from the electrode.
The lead wiring can be formed by the above-described method. For example, the lower electrode 24 and the upper electrode 26 are exposed without providing the piezoelectric layer 20 at an end portion of the piezoelectric film or a region protruding to the outside, and lead lines are provided so as to be connected to these portions. As another example, a lead line is provided by peeling the protective film and the electrode layer from the end portion of the piezoelectric film or the region protruding to the outside, and inserting a copper foil tape or the like between the piezoelectric layer 20 and the electrode layer. As another example, a lead line is provided by providing a through hole in a protective layer of a piezoelectric film at an end portion or a region protruding to the outside of the piezoelectric film, forming a conductive member in the through hole using conductive paste such as silver paste, and connecting a copper foil tape or the like to the conductive member.
Among them, the preferable thickness of the piezoelectric layer 20 of the piezoelectric thin film 12 is 8 to 300 μm, and is very thin. Therefore, in order to prevent short-circuiting, it is preferable that the lead lines be provided at different positions in the plane direction of the piezoelectric film. That is, the lead line is preferably provided offset (off set) in the surface direction of the piezoelectric film.
In the laminated piezoelectric element of the present invention, it is preferable that a protrusion protruding from the laminated piezoelectric element is provided on the piezoelectric film 12, and the lead line is connected to the protrusion.
For example, when the piezoelectric element 56A is laminated so that the folded portion of the piezoelectric film 10La extends along the longitudinal direction, as conceptually shown in fig. 13, a protruding portion 60 protruding in a convex shape may be provided at one end in the folding direction, and the lead line 62 and the lead line 64 may be connected to the protruding portion.
Further, when the piezoelectric element 56B is laminated so that the folded portion of the piezoelectric film 10Lb extends in the short-side direction, as conceptually shown in fig. 14, one end portion in the folding direction may be extended to form a protrusion 60, and the lead line 62 and the lead line 64 may be connected to the protrusion.
Further, when the piezoelectric element 56B is laminated along the short-side direction by the folded bending portion of the piezoelectric film 10Lb, as conceptually shown in fig. 15, a convex protruding portion 60 may be provided at an end portion in a direction orthogonal to the folding direction, that is, at an end portion in the long-side direction of the piezoelectric film 10Lb, and the lead line 62 and the lead line 64 may be connected thereto.
The protruding portion 60 may be provided on any one of the laminated piezoelectric thin films, but is preferably provided on the uppermost layer or the lowermost layer in view of piezoelectric efficiency and the like. The protruding portion may be provided in a plurality of layers such as the uppermost layer and the lowermost layer of the piezoelectric thin film and the uppermost layer, the intermediate layer, and the lowermost layer, or may be provided in all layers of the piezoelectric thin film. When the protrusion is provided in a plurality of layers of the piezoelectric thin films, the protrusion may be provided at the end in the short side direction of the laminated piezoelectric element or at the end in the long side direction, or the protrusion at the end in the short side direction and the protrusion at the end in the long side direction may be mixed.
In the laminated piezoelectric element according to the present invention, it is preferable that the protruding portion of the piezoelectric thin film protrudes from an end portion in the longitudinal direction of the laminated piezoelectric element, and the length of the protruding portion 60 in the longitudinal direction of the laminated piezoelectric element is 10% or more of the length in the longitudinal direction of the laminated piezoelectric element.
In the following description, the length of the protruding portion in the longitudinal direction of the laminated piezoelectric element is also simply referred to as "the length of the protruding portion".
When the protruding portion 60 is provided at the end portion of the laminated piezoelectric element in the short-side direction, the length of the protruding portion 60 in the short-side direction is preferably 50% or more of the length of the laminated piezoelectric element in the short-side direction.
A conceptual diagram of the laminated piezoelectric element 56B in fig. 16 will be specifically described.
The laminated piezoelectric element 56B is a laminated piezoelectric element in which a bending portion by folding of the piezoelectric film 10Lb is along the short side direction of the laminated piezoelectric element (refer to fig. 12 and 15). Therefore, as shown in fig. 16, the longitudinal direction of the laminated piezoelectric element 56B is a direction orthogonal to the folding direction of the piezoelectric film 10 La. That is, the longitudinal direction of the laminated piezoelectric element 56B coincides with the longitudinal direction of the piezoelectric thin film 10 Lb.
As shown in fig. 16, the length of the laminated piezoelectric element 56B in the longitudinal direction is L. In the present invention, the length La of the protrusion 60 is preferably 10% or more of the length L, i.e., "La. gtoreq.L/10".
Therefore, the current density in the path through which the drive current flows from the lead wiring to the laminated piezoelectric element is reduced, and thus the voltage drop can be reduced, and the piezoelectric characteristics can be improved. For example, the electroacoustic transducer can improve sound pressure.
The length La of the protruding portion 60 is more preferably 50% or more, still more preferably 70% or more, particularly preferably 90% or more, of the length L in the longitudinal direction of the laminated piezoelectric element, and most preferably more than the length in the longitudinal direction of the planar shape of the laminated piezoelectric element 56B.
Therefore, in the case of the laminated piezoelectric element 56A in which the folded bending portion of the piezoelectric film 10La shown in fig. 11 and 13 is along the longitudinal direction, it is preferable that one end portion in the folding direction is extended to be a protruding portion, and the lead line 62 and the lead line 64 are connected to the protruding portion, similarly to the laminated piezoelectric element 56B shown in fig. 14. At this time, the length La of the protruding portion coincides with the length L of the laminated piezoelectric element in the longitudinal direction. That is, in this case, the protruding portion is formed over the entire region in the longitudinal direction of the laminated piezoelectric element.
The piezoelectric film, the laminated piezoelectric element, and the electroacoustic transducer of the present invention have been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications can be made without departing from the scope of the present invention.
Examples
The present invention will be described in more detail below with reference to specific examples thereof.
[ example 1]
The piezoelectric thin film shown in fig. 2 was produced by the method shown in fig. 2 to 6.
First, a base material was dissolved in Methyl Ethyl Ketone (MEK) at the following composition ratio. Thereafter, PZT particles were added to the solution at the following composition ratio, and dispersed by a propeller mixer (rotation speed 2000rpm), thereby preparing a coating material for forming a piezoelectric layer.
PZT particles … … 1000 parts by mass
… … 100 parts by mass of base Material
MEK … … 600 parts by mass
In addition, the PZT particles are prepared by sintering commercially available PZT raw material powder at 1000 to 1200 ℃ and then pulverizing and classifying the powder until the average particle size becomes 3.5 μm.
Also, cyanoethylated PVA (CR-V, Shin-Etsu Chemical Co., Ltd., manufactured by Ltd.) and cyanoethylated polytriacose (CR-S, Shin-Etsu Chemical Co., manufactured by Ltd.) were used as the base material. Regarding the amount ratio of the two in the matrix, cyanoethylated PVA was 40 mass%, and cyanoethylated polytriglucose was 60 mass%.
On the other hand, a sheet as shown in FIG. 2 was prepared by vacuum-depositing a copper thin film having a thickness of 0.1 μm on a long PET film having a width of 23cm and a thickness of 4 μm. That is, in this example, the upper electrode and the lower electrode were copper deposited films having a thickness of 0.1m, and the upper protective layer and the lower protective layer were PET films having a thickness of 4 μm.
In order to obtain a good operation in the process, the film electrodes and the protective layers were thermocompression bonded using a PET film with a separator (dummy support PET) having a thickness of 50 μm, and then the separator of each protective layer was removed.
The coating material for forming the piezoelectric layer prepared previously was applied on the lower electrode (copper vapor-deposited film) of the sheet using a slide coater. The coating material was applied so that the film thickness of the dried coating film became 40 μm.
Next, the object coated with the coating on the sheet was dried by heating in an oven at 120 ℃, thereby evaporating MEK. Thus, a laminate having a lower electrode made of copper on a lower protective layer made of PET and a piezoelectric layer having a thickness of 40 μm formed thereon was produced as shown in fig. 3.
The piezoelectric layers of the laminate were subjected to polarization treatment in the thickness direction by corona polarization as shown in fig. 4 and 5. The temperature of the piezoelectric layer was set to 100 ℃, and a dc voltage of 6kV was applied between the lower electrode and the corona electrode to generate corona discharge, and thus polarization treatment was performed.
As shown in fig. 6, the laminate subjected to the polarization treatment was laminated with the same sheet-like material obtained by vacuum vapor-depositing a copper film on a PET film.
Next, the laminate of the laminate and the sheet was thermally pressed at 120 ℃ by a laminating apparatus, whereby the piezoelectric layer was bonded to the upper electrode and the lower electrode, the piezoelectric layer was sandwiched between the upper electrode and the lower electrode, and the laminate was sandwiched between the upper protective layer and the lower protective layer.
Thus, a piezoelectric thin film shown in fig. 1 was produced.
For the piezoelectric thin film thus produced, a test piece in the form of a 1 × 4cm strip was produced to measure the dynamic viscoelasticity, and the loss tangent (tan δ) at a frequency of 1Hz was measured.
The measurement was performed using a dynamic viscoelastometer (manufactured by SII NanoTechnology inc., DMS6100 viscoelastometer).
The measurement conditions were set to a measurement temperature range of-50 to 170 ℃ and a temperature rise rate of 2 ℃/min (in a nitrogen atmosphere). The measurement frequencies were set to 0.1Hz, 0.2Hz, 0.5Hz, 1Hz, 2Hz, 5Hz, 10Hz, and 20 Hz. The measurement mode is set to the tensile measurement. Further, the chuck pitch was set to 20 mm.
As a result, the loss tangent of the piezoelectric thin film at a frequency of 1Hz was in a temperature range of more than 50 ℃ and 150 ℃ or less, and had a maximum value (maximum value) of 0.34 at 100 ℃.
The loss tangent of the piezoelectric thin film at a frequency of 1Hz and 50 ℃ was 0.1.
Comparative example 1
In the coating material for forming the piezoelectric layer, concerning the amount ratio of the materials in the base material, cyanoethylated PVA was set to 70 mass%, and cyanoethylated polytriglucose was set to 30 mass%. A piezoelectric thin film was produced in the same manner as in example 1, except that this coating material was used.
With respect to the piezoelectric thin film thus produced, the loss tangent at a frequency of 1Hz was measured in the same manner as in example 1.
As a result, the loss tangent of the piezoelectric thin film at a frequency of 1Hz was in a temperature range of more than 50 ℃ and 150 ℃ or less, and had a maximum value (maximum value) of 0.09 at 80 ℃. The loss tangent of the piezoelectric thin film at a frequency of 1Hz and 50 ℃ was 0.2.
Comparative example 2
In the coating material for forming the piezoelectric layer, the base material was cyanoethylated polyglucose 100 mass%. A piezoelectric thin film was produced in the same manner as in example 1, except that this coating material was used.
With respect to the piezoelectric thin film thus produced, the loss tangent at a frequency of 1Hz was measured in the same manner as in example 1.
As a result, the loss tangent of the piezoelectric thin film at a frequency of 1Hz was in a temperature range of more than 50 ℃ and 150 ℃ or less, and had a maximum value (maximum value) of 0.45 at 120 ℃. The loss tangent of the piezoelectric thin film at a frequency of 1Hz and 50 ℃ was 0.06.
The flexibility of the piezoelectric thin film thus produced was evaluated as follows.
Using a round bar made of iron, a bending test of 10000 times 180 ° folding was performed so that the radius of curvature of the central portion of the vibration plate became 5 cm. Further, the flexibility was evaluated in 2 temperature environments of high temperature (100 ℃) and normal temperature (25 ℃).
A was evaluated as the case where peeling did not occur at any interface even when the bending test was performed 10000 times;
evaluating the condition that peeling occurs at any interface during 1000-9999 times of bending tests as B;
the case where peeling occurred at any interface during the bending test period of 999 times was evaluated as C;
the results are shown in the following table.
[ Table 1]
As shown in table 1, the piezoelectric thin film of the present invention having a loss tangent at a frequency of 1Hz, which has a maximum value of 0.1 or more in a temperature range of more than 50 ℃ and 150 ℃ or less and a value of 0.08 or more at 50 ℃ has excellent flexibility in a high temperature range and also has good flexibility in a normal temperature range.
On the other hand, the piezoelectric thin film of comparative example 1 having a loss tangent at a frequency of 1Hz of 0.08 or more at 50 ℃ and a maximum value in a temperature range of more than 50 ℃ and 150 ℃ or less, but the maximum value of less than 0.1 has excellent flexibility in a normal temperature range, but has lower flexibility in a high temperature range than the present invention.
Further, the piezoelectric thin film of comparative example 2, in which the loss tangent at a frequency of 1Hz had a maximum value of 0.1 or more in a temperature range of more than 50 ℃ and 150 ℃ or less and a value at 50 ℃ was less than 0.08, had excellent flexibility in a high temperature range, but had low flexibility in a normal temperature range.
From the above results, the effects of the present invention are remarkable.
Industrial applicability
The present invention can be preferably used for various applications such as acoustic equipment including speakers and microphones, and pressure sensors.
Description of the symbols
10. 10L, 10La, 10 Lb-piezoelectric film, 10a, 10 c-sheet, 10B-laminate, 12-vibration plate, 14, 56A, 56B, 61-laminated piezoelectric element, 16, 19-adhesive layer, 20-piezoelectric layer, 24-lower electrode, 26-upper electrode, 28-lower protective layer, 30-upper protective layer, 34-base, 36-piezoelectric particles, 40-corona electrode, 42-DC power supply, 43-housing, 45-piezoelectric speaker, 46-viscoelastic support, 48-frame, 50-electroacoustic transducer, 58-core rod, 60-protrusion, 62, 64-lead-out wiring, PS-power supply.
Claims (13)
1. A piezoelectric thin film characterized in that,
the piezoelectric thin film has a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix containing a polymer material, and electrode layers formed on both surfaces of the polymer composite piezoelectric body,
the loss tangent at a frequency of 1Hz obtained by dynamic viscoelasticity measurement has a maximum value of 0.1 or more in a temperature range of more than 50 ℃ and 150 ℃ or less, and the value at 50 ℃ is 0.08 or more.
2. The piezoelectric thin film according to claim 1, which has a protective layer provided on a surface of the electrode layer.
3. The piezoelectric thin film according to claim 1 or 2, which is polarized in a thickness direction.
4. The piezoelectric thin film according to any one of claims 1 to 3, which has no in-plane anisotropy in piezoelectric characteristics.
5. The piezoelectric thin film according to any one of claims 1 to 4, which has an external lead for connecting the electrode layer with an external power source.
6. A laminated piezoelectric element obtained by laminating 2 or more piezoelectric thin films according to any one of claims 1 to 5.
7. The laminated piezoelectric element according to claim 6,
the piezoelectric films are polarized in the thickness direction, and the polarization directions of the adjacent piezoelectric films are opposite.
8. The laminated piezoelectric element according to claim 6 or 7, wherein the piezoelectric thin film is laminated by 2 or more layers by folding the piezoelectric thin film 1 or more times.
9. The laminated piezoelectric element according to any one of claims 6 to 8, having an adhesive layer that adheres adjacent piezoelectric films.
10. An electroacoustic transducer having a vibration plate and the piezoelectric film according to any one of claims 1 to 5 or the laminated piezoelectric element according to any one of claims 6 to 9.
11. The electro-acoustic transducer of claim 10,
the product of the thickness of the piezoelectric film or the laminated piezoelectric element and the storage modulus at a frequency of 1Hz and 25 ℃ obtained by dynamic viscoelasticity measurement is 0.1-3 times of the product of the thickness of the vibrating plate and the Young modulus.
12. The electro-acoustic transducer of claim 10 or 11,
the product of the thickness of the piezoelectric film or the laminated piezoelectric element and the storage modulus at 25 ℃ at a frequency of 1kHz on the main curve obtained by dynamic viscoelasticity measurement is 0.3-10 times the product of the thickness of the vibrating plate and the Young's modulus.
13. The electro-acoustic transducer according to any one of claims 10 to 12, which has an adhesive layer that adheres the vibration plate to the piezoelectric film or the laminated piezoelectric element.
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| PCT/JP2020/014097 WO2020196850A1 (en) | 2019-03-28 | 2020-03-27 | Piezoelectric film, layered piezoelectric element, and electroacoustic transducer |
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| JP7206294B2 (en) | 2018-11-08 | 2023-01-17 | 富士フイルム株式会社 | Laminated piezoelectric element and electroacoustic transducer |
| KR20220100013A (en) * | 2019-12-18 | 2022-07-14 | 후지필름 가부시키가이샤 | piezoelectric film |
| CN112366272B (en) * | 2020-10-28 | 2022-07-01 | 业成科技（成都）有限公司 | Piezoelectric induction component and manufacturing method thereof |
| CN113285631A (en) * | 2021-06-29 | 2021-08-20 | 陕西科技大学 | Piezoelectric nano generator with laminated structure |
| JPWO2023021944A1 (en) * | 2021-08-20 | 2023-02-23 | ||
| CN117981356A (en) * | 2021-09-24 | 2024-05-03 | 富士胶片株式会社 | Piezoelectric element and piezoelectric speaker |
| CN118020316A (en) * | 2021-09-28 | 2024-05-10 | 富士胶片株式会社 | Piezoelectric element and piezoelectric speaker |
| KR102711323B1 (en) * | 2021-12-23 | 2024-09-27 | 가천대학교 산학협력단 | manufacturing method of piezoelectric sensor based on flexible conductive polymer, piezoelectric sensor manufactured by using the same manufacturing method, and sensing method of the same piezoelectric sensor |
| JPWO2023153126A1 (en) * | 2022-02-10 | 2023-08-17 | ||
| WO2023248696A1 (en) * | 2022-06-24 | 2023-12-28 | 富士フイルム株式会社 | Piezoelectric film, piezoelectric element, electroacoustic transducer, and method for manufacturing piezoelectric film |
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| JP6196400B2 (en) * | 2015-01-29 | 2017-09-13 | 富士フイルム株式会社 | Electroacoustic conversion film |
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| WO2014157684A1 (en) * | 2013-03-29 | 2014-10-02 | 富士フイルム株式会社 | Speaker system |
| WO2014162976A1 (en) * | 2013-04-01 | 2014-10-09 | 富士フイルム株式会社 | Electroacoustic transduction film |
| WO2017002573A1 (en) * | 2015-06-29 | 2017-01-05 | 富士フイルム株式会社 | Electro-acoustic converter |
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